I grew up playing Quake II somewhere around 1997-99 and I think the game still holds up today. I was really looking forward to Quake 4 but I do not think it compares well to the original for a number of reasons.
- Bad vehicle and on-rail sections. During the game there are a few sections where you have to pilot a hover-tank, a mech, and man a machine gun. They were not only less interesting than the rest of the game, they were actually quite harder. I didn't have much trouble with the difficulty throughout the rest of the game, but these sections I found myself cheating through because I couldn't get past them. Had they been overly-difficult, but also very fun, it would have been a different story. The vehicle sections consist of mostly straight paths where you can just skip past most of the enemies. The environments were rather empty (and ugly) because of the increased scale. Driving the tank wasn't so bad, but the mech was just slow and plodding. The on-rails segments actually didn't start off too bad. You were defending a convoy and protecting an engineer who had to disarm mines. After that though, you had to shoot down missile pods before they shot heat seeking missles at you and it became very difficult. Same goes for the second tram ride mounted machine gun mission later in the game.
- Inferior aesthetics. This is a more subjective category, but Quake 4's art didn't match Quake II's. The changes made were partly due to technology. Lack of polygons in the models in Quake 2's caused the designers to have to work around this so many art assets had flat sides. This is in-part why the game looked cool. Everything in Quake 4 was rounded off some what unnecessarily. All of the grunt enemies had these badass face shields in Quake 2 but in Quake 4, they're all bald, Colin-Mochre looking mother effers. The Tank bosses used to have flat armor plates and were big and mean looking but now they're round and boring. The original model looked much less human and more like "Let's give this tank legs and a human? face." The origional shotgun (probably one of the greatest shotguns in video game history) looked like you were firing a book. Now it's just "ugly green shotgun with LCD on back". It's hard to put into words, but most of the enemies and weapons are just ugly and don't have the same punch that they did in Quake II. This is less of a big deal but Stroggos in Quake 2 was far less dry than it was in Quake 4. Q4 Stroggos was a giant desert but Q2 Stroggos had a lot of water and some mossy looking grass every so often. All of the humans had weird heads.
- Super lame final boss. Spoilers here. The last boss fight is fighting the Makron again. It's more or less the same fight you had with him in the middle of the game except he can summon enemies. Then you have to blow up a giant brain. This all takes place in an incredibly generic brown room, made worse by the rather interesting architecture in the level before the boss fight.
- Where is the BFG? Instead of giving you another BFG, they give you a Dark Matter Gun which is basically the same thing except it sucks guys up instead of shooting a big "ball of death".
- Nerfing the railgun. In the name of realism, all of the guns in the game were given clips. This is good, and to be expected but the clip size for the railgun was three slugs. Was that really necessary? It fires so slow that you could have just assumed it was reloaded after every shot.
The game was not without its good points
- Brining back some Quake weapons. It was pretty cool to see the return of the nail gun and the lightning gun, even though we did see it in Quake 3.
- A couple scenes. After a hectic period of the game (I think it might have been after that first on-rails segment), a large human spaceship lands out in a field and you enter it. It's a nice break in the action and there are some interesting scripted events involving Strogg biology and human technology. Also, I thought the infamous transformation scene was pretty awesome/terrible and very hard to watch. Games usually don't make me want to turn away because I can't take what's going on in a cutscene.