I liked it.
I'm
not one for single player fps. I liked Quake 1 (especially Team Fortress), Q2, and loved Q2 Rocket Arena. I played Q4 last night 1 vs 1 just on a LAN and was impressed. It's pretty heavy on the requirements though. First,
it will not run on win98. The Doom 3 "registry hack" doesn't work. I had to grab a drive and install XP on my "gaming rig"

just because of this. It's an older machine:
AMD 2400+ XP
2x 256mb of corsair memory (mobo doesn't support the dual-channel though)
256mb ATI (9600?)
7200rpm HDI did the auto-detect and it set stuff as "low". I bumped the resolution to 800x600 and it played without a stutter. My friend used his laptop:
Intel ? (I know the Mhz equiv is less than mine)
256mb video card
512 memoryHe had it installed first and noticed some stuttering on single player with "medium" settings. He changed it to low (& 800x600 widescreen), and the stuttering stopped. I used his cdkey and I hosted while he connected to me. There were some hurdles to jump through to get us connected with the same cdkey (and that's all I'm going to say about that).
I didn't try single player (and probably never will). He did and wasn't that impressed, but his taste is exactly like mine when it comes to games. He said it was
very similar to how Doom 3 feels.
The multiplayer maps include some new & some remakes from previous quake titles, we kind of stuck to playing the ones from Q2 because neither of us were real impressed with Q3, and we played Q2 longer than Q1. It seems like you run faster than in Q2 and the maps have more color/flavor. Overall, it's good. Good enough for me to buy it so we can play online together. I was real concerned about the hardware requirements, but it looks like I'll be good for now, and can update slowly like I usually do. If you're the type that needs to see every effect with all it's glory, you'll need a pretty heavy-hitting machine.
Guns (that I remember):
Cutter- Think Unreal disc thrower, but handheld. Like Q1's Axe.
Lightning- Just like Q1
Shotgun- Like Q2
Grenade Launcher- Like Q2, but longer detonation time
Rocket Launcher- Like Q2, seems like smaller blast radius?
Rail Gun- Like Q2, straight, no cool coil look

. Seems easier to hit? Might just be the maps? Seems like less damage. Easier to pick out where the shot is from.
Nail gun- Shreds the ^%$# out of people. This is a choice weapon IMO.
The maps are higher contrast. There are areas that are lit up pretty good. There is also a LOT of movement in the maps which makes it difficult to tell at first if it's a person or something that belongs there. Knowing the map will be an advantage (as always). Nice color, nice effects. Should look real good with the right hardware. The lighting will make you cast a shadow so you might blow yourself up a few times thinking someone is there. I did

.
RANT: Let's be honest about minimum requirements. The minimum requirements were met by my friends laptop and even on the low setting there was some stuttering in single player. The minimum req's should be the point where the game is
enjoyable *cough* no stuttering *cough*. NOT just "playable". My friend is a tech and knows computers and if
he can't get it to work stutter-free with the minimum req's, than the average user that has 100 things in the background will
never get it to work right. Luckily, he and I remember how to tweak settings, so we'll get it to play well. Joe Average will need to upgrade his machine though (or wait for some tweaks to be posted).
RANT2: Since when did planetquake require you to pay? How stupid. That site helped carry Quake into the game that it was. If Q4 is going to be as popular as Q2, there needs to be some sites where maps, skins, models, etc can be downloaded without charge. Whether id does this or not, it doesn't matter. All I know is that I'm not paying more to play a $50 game. I'll go back to Counter-Strike or Q1/Q2.
In summary: Think Q2 remake with more speed and more colors. I'm buying it and I liked: Q1 & Q2 much more than Q3 or UT. I'll be running it on the machine listed above.