I've been playing Ghost Recon (online coop) since about 2002. Not only is the game really good, the AI even on medium can be a decent challenge. I do agree that it's unrealistic that enemy can pick you off with a pistol at over 100 yards, and your team AI isn't very useful. When this game came out, the AI was better then most FPS out there (2001) for it's time.
IMHO, multiplayer is better then doing missions by yourself with team AI. Get on with a few people, then do missions, or go head to head.
With Modern day computers (this game was to run on a 450 P II) you can crank up the video quality. game still looks pretty good compared to games today. Also, it was designed to run over dial-up (so even poor DSL or Cable internet works just fine). You can put up your own 'play and serve' game for other people to get on with you.
Personally, I think this why the game is great compared to some modern games - You don't have to register with UBI, and then go to their server, No 'Pay to Play', etc. You can easily serve and play, or run a dedicated server. You put up your own game, and people connect to you directly. (we use Ventrilo to voice chat while playing).
Also if you get bored with the maps and missions, there are still tons of mods listed on websites out there - HX5 mod, DA 4.9 (Dark Angels), Frostbite, Badlands Sniper, Navy Seals, DVS1 weapons mod, Dangerous Babes, and tons of others (Mods are in the hundreds). Not mentioning all the maps out there.
If that doesn't get ya, there is a editor (igor.exe) for the game. You can create maps, edit the guns, kits, alter the explosion to 'nades, increase the loads and much more.
I've managed to make the 'Nades blow up bigger (20 instead of 5 meters) change magazines to hold 50 rounds instead of 30, and some to hold 100 (like a C-mag). I've also shortened the 'zero' times, and I've increased things in the kits like Nades - 10 or 12 instead of just getting 6.
You can play missions (coop) TDM, KotH... and all the other usual styles, and with HX5 mod, you can go up against 140 to 200 bots. Choose your map, get your guns, and then watch the bullets fly.
Tons of mods, great gameplay, not demanding on hardware, and still pretty good graphics. This game never gets old.