if you have any? are there even places that host q2 maps anymore? 

I've never played any q2sp's either but will check out that one for sure! 

i'd like to check some quality q2sp maps 

first and foremost, get grinspq1-3: castles of stroggos - it's like the q2/tech equivalent of the mexx bishop trilogy. the first one isn't amazing but it's worth it for completeness' sake; the third one is absolutely fantastic, one of my favourite ever FPS experiences :)

some others that spring to mind;

angron2: premonition of angron
psph20: the powershere quest (coop episode, use skill 0 for single player otherwise it's insanely hard)
genome: prognetto genome (bit hordey at times but visually stunning)
du: dark undergrowth
1964com: echoes of the past
strike: retaliatory strike
ddb: deaf, dumb and blind
batf: back at the front

most of those can be found here: http://www.gamers.org/pub/idgames2/planetquake/ltdan/ - google should suffice for any that can't :) 

some of these overlap with rj's recommendations but this is the cream of the q2sp crop IMHO (in alphabetical order):

1964 Echoes of the Past
Amari Aliquid
Awakening (mod)
Back at the Front
Castles of Stroggos (gets better in build quality, ep3 is phenomenal)
Citizen Abel 3
Citizen Abel 4
Dark Undergrowth
Deaf, Dumb and Blind
Last Day on Stroggos
Light (needs awakening mod)
Love Story of the Prince of Stroggos
Machine Reborn
Monumental Misery
Nightmare Orchards
Premonition of Angron
Retaliatory Strike
Spogsp1
Space Odyssey 2
Space Odyssey 3
Space Odyssey 4
The Widening Gyre
What the End is For 

there was some guy of the quake sadlark fame whos been working on episode/unit some time ago. what happened with him? 

sequel to Angron, lost it in HD crash I believe.

The only q2sp still being worked on, or was, was Musashi's map pack :

http://musashi.backshooters.com/index.html

But last update was Jan 2010. Maybe Maric knows? 

http://tenfourmaps.telefragged.com/php/revidx.php?gameid=q2&sortby=award&page=1 

But the one's I'd pick out as special favourites;

Citizen Abel Series
Light (Needs Awakening mod)
The Widening Gyre
Spogsp1

And anything made with the Lazarus mod - even its test maps in a series of abandoned warehouses are fun.

There was one Lazarus map pack, I think it was called Garage Inc - that was pretty good. 

There is one missing off those lists:

Strogg Towers by Daz 

 

Another one you should definitely try is 'Wierd Comic Art Quake2'. 

I used to play Q2 custom maps, and checked almost every recommended one, but I never really liked how Q2 plays.
Overall balance, monsters, slow weapon switching and other timing effect - everything seems off making it much slower and less fun game than older shooters (Doom, Quake, Duke etc) 

i wanted to elaborate a bit on COS3 this morning but didn't have time. it's actually my favourite custom release of any FPS game. the whole thing has an amazing edge-of-seat atmosphere with great use of dark shadows and ambient sounds, and it really plays to q2's strengths by not relying on fast-paced action & horde combat; instead carefully limiting supplies and ensuring every enemy confrontation is properly staged. it's dark, tense and scary, but ultimately thoroughly satisfying.. best experienced in the dark with headphones :)

i last played it mid last year during a break from doom3, which i was in the middle of at the time. there was one moment that struck me as twice as scary as anything d3 could manage, where you navigate a long corridor followed by a huge warehouse type room full of crates, all the time with very limited health, and for a full few minutes you can hear the constant tapping of a parasite's foot. it's hard to make out the direction or distance it's coming from and you'll creep through the warehouse thinking it's round every damn corner, finding out it isn't, breathing a sigh of relief and tensing back up again as you creep forward. such a simple, subtle and effective technique to put the player on edge 

you can hear the constant tapping of a parasite's foot.

that was something i noticed when playing spogsp1... q2 monsters are noisy mofos. i kind of just rolled my eyes near the end of the map with all the iron maiden moaning... thank god they didn't replicate that in q4. :P 

Grinspq2 or grinspq3 that has that heavy alien vibe? 

i have no doubt alien inspired much in both of them :) 

From the screenshots, though I'm sure I've played them.

Time to reinstall Q2? 

but I never really liked how Q2 plays

Yeah, its not as good as Quake. Too slow, not inventive enough with the monsters, although level design was top notch.

I would have liked it much better with less humanoid enemies.

Gladiator, parasite, medic brain in a jar were all cool whilst things like the icarus (why give it legs) and Enforcer (that fall over shooting thing got old quickly) just looked silly.

Gunner was cool I suppose, but he the humanoid should have been few and far between. Imagine if the three basic troopers were instead quadrupedal, or if there was an arachnid crate loader creature.

The Makron was awesome. The shitty railgun head thing (humanoid again) that popped out was like a a Kinder Surprise having a turd in it. 

the shitty railgun head thing was the makron. the thing that held it was called jorg, i think 

Who's fault is it when centerprints are not send to all coop clients? Played id1 with quakespasm (both dedicated server and clients). 

Is quite funny that in PC Quake 2 the final boss is piss easy but on the playstation it was rock hard (not just because of worse controls either) 

Also yeah Quake 2 everything was too slow. The Tanks were pathetic really, compared to a Shambler. And nothing Fiend like either really :E 

But it was so big it got stuck on everything. 

too many hitscan enemies, too many slow, high-HP enemies, and then the ones that were effective were often TOO effective, i.e. the gunner grenade spam. And i don't like the feel of the weapons as much.

My favorite was probably the bezerker, he was kind of a beefed-up quake knight -- rush the player and melee, but with enough health that you had to backpedal as you fought him. That was sort of the model for my rubicon2 dreadmaughts, actually.

I also like the flyer since it requires careful aim, but you also have to periodically side-step his attack, which throws off your aim again.

Parasite was a good panic-inducer, like the tarbaby -- not exactly fun to fight, but a good tool to make the player feel less in control.