Back when I was just a wee lad in high school, a bunch of my friends and I used to stay at one of our friends' house that had immaculate soundproofing and play Xbox for hours. In my estimates, at least three complete playthroughs of the original Halo occurred there in one year. On a whim I asked someone to pick up a copy of Serious Sam, the Xbox release. To this day, I've insisted on keeping my copy of the game, and do break it out for a playthrough every once in a while. That being said, when a HD re-release of the original Serious Sam, I was excited. Then it came out, and I was very very poor for a long time. Now that I have a little more financial wiggle room, I picked the game up. Here's what I thought of it. 

First, it's very important to note that, regardless of branding, of level design, of similarities of enemies and likenesses of heroes, and of audio - this is a completely different game than the original Xbox release. The original release was a cartoony FPS awarding points for enemy kills, allowing the player to earn extra lives by collecting enough points, and sporting humorous references to games and movies in ridiculous voiceovers. Even the menus boasted bouncing lettering and the ability to have "hippy" blood where enemies' arterial spray was replaced with flowers. The character's proportions were way off and the enemy design seemed tongue-in-cheek.

My fun friend has been replaced with a battle-hardened competition-driven FPS where players duke it out on the leaderboards for point-based dominance. Players have no extra lives - a death is a "game over" screen. The new game sports a severe green and black lettering menu more reminiscent of The Matrix than the original game. Next to the lettering on the left is an image of a proportionate, yet cut hero. Instead of ridiculous pecs, Sam now has a mouth that leaves you wondering whether his head was cut in half, then reassembled while watching The Dark Knight. In game, the character still makes the same sarcastic comments, sports a "hippy" blood mode, and inquires as to how "serious" the player is when choosing menu itema, but I can't help thinking that it's purely in lip service to the original game.

The graphics are perhaps this game's redeeming quality - they're gorgeous. I find it ironic that a title debuting close to 10 years ago has been rebooted to have better graphics than most FPS games out there (save for Killzone 3 and a few others.)

While the game's controls have been pretty greatly streamlined, I noticed there was a quick-save button. My initial thoughts were "wow, Croteam had too many buttons and just decided to throw some random functions in there." About 3 hours and 60 deaths later, I knew why they decided on that button mapping scheme. In terms of enemies, the skeleton enemies that gallop and Sam, stopping occasionally to hurl bolo cannonballs now take a dead-on super shotgun shot to fell on normal difficulty, and even take more than one regular shotgun shot on easy. In the original game, these enemies collapsed with one square shot with the normal shotgun on normal - simply put, what was "normal" on the original release is now considered "tourist" in this release.

So, there are two criterion that are inevitably taken into account when evaluating this game: how it plays as a remake of the original Serious Sam, and how it functions on its own. Compared to the original, its obvious Croteam wanted closer to a "reboot" than an "HD remake." It's a fundamentally different game and experience which forces it to shed its irony with regards to the title, instead embracing the "seriousness" of absurd enemy hordes. If I were to give it a numerical score on likeness to the original, it might get a 1 or a 2 out of 5 at the very most. As its own game, it's another story. The game is hard... very hard. However, it is rewarding to know you survived a ludicrous onslaught that only the most resourceful and steady-handed FPS fans should survive. As an a brutal arcade FPS which alienates its more clever references in favor of a new breed of hardcore shooter fans, the game succeeds. At the end of the day, when you download a trial of this game and it asks whether you're serious, you can safely buy the game if you would answer "yes."     
 
Edit: After playing a considerable amount of co-op in the recent past, it's obvious that this is where the game is the most similar to the original release. 

Back when I was just a wee lad in high school, a bunch of my friends and I used to stay at one of our friends' house that had immaculate soundproofing and play Xbox for hours. In my estimates, at least three complete playthroughs of the original Halo occurred there in one year. On a whim I asked someone to pick up a copy of Serious Sam, the Xbox release. To this day, I've insisted on keeping my copy of the game, and do break it out for a playthrough every once in a while. That being said, when a HD re-release of the original Serious Sam, I was excited. Then it came out, and I was very very poor for a long time. Now that I have a little more financial wiggle room, I picked the game up. Here's what I thought of it. 

First, it's very important to note that, regardless of branding, of level design, of similarities of enemies and likenesses of heroes, and of audio - this is a completely different game than the original Xbox release. The original release was a cartoony FPS awarding points for enemy kills, allowing the player to earn extra lives by collecting enough points, and sporting humorous references to games and movies in ridiculous voiceovers. Even the menus boasted bouncing lettering and the ability to have "hippy" blood where enemies' arterial spray was replaced with flowers. The character's proportions were way off and the enemy design seemed tongue-in-cheek.

My fun friend has been replaced with a battle-hardened competition-driven FPS where players duke it out on the leaderboards for point-based dominance. Players have no extra lives - a death is a "game over" screen. The new game sports a severe green and black lettering menu more reminiscent of The Matrix than the original game. Next to the lettering on the left is an image of a proportionate, yet cut hero. Instead of ridiculous pecs, Sam now has a mouth that leaves you wondering whether his head was cut in half, then reassembled while watching The Dark Knight. In game, the character still makes the same sarcastic comments, sports a "hippy" blood mode, and inquires as to how "serious" the player is when choosing menu itema, but I can't help thinking that it's purely in lip service to the original game.

The graphics are perhaps this game's redeeming quality - they're gorgeous. I find it ironic that a title debuting close to 10 years ago has been rebooted to have better graphics than most FPS games out there (save for Killzone 3 and a few others.)

While the game's controls have been pretty greatly streamlined, I noticed there was a quick-save button. My initial thoughts were "wow, Croteam had too many buttons and just decided to throw some random functions in there." About 3 hours and 60 deaths later, I knew why they decided on that button mapping scheme. In terms of enemies, the skeleton enemies that gallop and Sam, stopping occasionally to hurl bolo cannonballs now take a dead-on super shotgun shot to fell on normal difficulty, and even take more than one regular shotgun shot on easy. In the original game, these enemies collapsed with one square shot with the normal shotgun on normal - simply put, what was "normal" on the original release is now considered "tourist" in this release.

So, there are two criterion that are inevitably taken into account when evaluating this game: how it plays as a remake of the original Serious Sam, and how it functions on its own. Compared to the original, its obvious Croteam wanted closer to a "reboot" than an "HD remake." It's a fundamentally different game and experience which forces it to shed its irony with regards to the title, instead embracing the "seriousness" of absurd enemy hordes. If I were to give it a numerical score on likeness to the original, it might get a 1 or a 2 out of 5 at the very most. As its own game, it's another story. The game is hard... very hard. However, it is rewarding to know you survived a ludicrous onslaught that only the most resourceful and steady-handed FPS fans should survive. As an a brutal arcade FPS which alienates its more clever references in favor of a new breed of hardcore shooter fans, the game succeeds. At the end of the day, when you download a trial of this game and it asks whether you're serious, you can safely buy the game if you would answer "yes."     
 
Edit: After playing a considerable amount of co-op in the recent past, it's obvious that this is where the game is the most similar to the original release. 

What on earth are you talking about? The original Serious Sam games and the HD remakes are pretty much identical in every way. At least the PC versions are. I didn't even know there was an Xbox port, but if what you're saying is true then I guess that one is a bit different.

My whole argument I was making was despite the fact that it was supposed to be a straight HD remake of the original games, there is a lot in the feel of the game which makes it a fundamentally different game. 

Tordah is right.  The original PC versions of TFE and TSE are almost 100% identical to the HD remakes, and I say this as a very discerning person who has played quite a lot of Serious Sam over the years.  While the art style and attitude was definitely tongue-in-cheek, none of the character designs had exaggerated proportions (save one, and he's only in TSE) that do not in the HD games, and while colorful and stylized, the games were far from cartoonish (contrary to Serious Sam 2 where there was a sweeping tonal shift toward cheesy cartoonishness and wacky flippancy, which I and a vast portion of previous SS fans haaaated with a Goddamn passion).  The way you describe Sam in the XBOX versions of the games as being weirdly proportioned sounds like how he was in SS2, which disgusted me.  The original Sam looked fairly close to how he does in the HD games, though his facial appearance and build aren't directly analogous. 
 
The original games also did not have some of the mechanical stuff you speak of.  Extra lives did not exist - those too were not introduced to the franchise on PC until SS2, which I also did not like.  The pump-action shotgun was only capable of killing Kleers in one shot in TSE; TSE's enemies had lowered resilience compared to TFE at corresponding difficulties.  Both TFE HD and TSE HD have the original enemy resilience of TFE, however.  Also, this goes without saying perhaps, but quick save has always been in the PC versions of all Serious Sam games.
 
What you're playing of the HD games is exactly how the original games on the PC were with minor cosmetic differences (menus were a bit more stylized, but not as much as you describe; some enemy designs have been very slightly altered or added to; some lighting changes in specific environments here and there; etc.).  There was no leaderboard, either (2001, yo).  Oh, they also have more in-depth physics on loose objects, so while the giant boulders for instance used to just follow static, preset paths, they now roll chaotically with physics acting on them and may not follow the same path every time.  Other than that, there's absolutely nothing different whatsoever.  They are exact replications of the original games.  The XBOX versions were the defectors, from the sounds of it.

Ah, ok. Yeah, it sounds like the XBOX port was something of an anomaly.