A solid product that feels unfinished.
Let's get the basics out of the way right now. This is not a complicated game. If you are capable of moving your character and firing a weapon at the same time, you can enjoy Serious Sam. That's not a slam on the game, if anything it's praise. It's refreshing to go back to straight shoot em up gameplay after so long. The game breaks down to going into an area, shooting all the bad guys, moving to the next area, and shooting those bad guys, and repeating that cycle until the level ends. As much as I adore this series, it really is a fancy shooting gallery. As such, quite a few gamers will probably want to seek their shooting fun elsewhere.
Serious Sam HD is a remake of Serious Sam: The First Encounter, and it's a damn good one. I played through the original before playing this, and it's amazing how well they did recreating everything. Even the old-school loading screen of a simple green bar on a black background remains. All of the objects, environments, enemies, and weapons are beautiful in their updated appearance, and on my merely adequate rig I experienced absolutely no slow down, regardless of how many enemies were on screen.
The controls are standard FPS fare, minus a reload key, which isn't an issue for the most part, but it's odd considering the original let you reload your revolver at any time (None of the other weapons require reloading), and as someone who does a lot of long range shooting with them early on, it was a bit of a pain to start shooting and suddenly have to sit through the reload animation. Other than that, there really is nothing to mention here. If you've played any FPS on a PC, you've used these controls before.
My only problems with the game are that it feels like they forgot some of the content. What's here is great, and will satisfy anyones trigger finger, but the multiplayer options are limited to a rather poorly done co-op, and while it is exhilirating taking on the entire campaign with up to 16 players, there are no dedicated servers, meaning your enjoyment depends entirely on how good the hosts internet is. Add to that what seems like poor netcode, and it makes co-op more trouble than it's worth. On my 1.5 MB/s connection, with only one other player in the game with me, the average ping was about 250.
Adding on to that, there is no competitive multiplayer. You're limited to either playing the campaign alone, or with some other people. That's it. As fun as the campaign is, this series has always felt like it could have some great deathmatch, and it feels like a big missed opportunity. In the end, Serious Sam HD is a good game. It's just that with gameplay so simple, and some lackluster features, only existing Sam fans will have any real incentive to pick this up.