As great as Half-Life 2; it isn't just Gmod but worse; just more simpler and without all the clutter that comes with that. It holds up on it's own just to screw around with the physics engine and that's all it needs to be really. There are a few good community servers for playing the game; my favourite probably being the Fusionhead Jazz Club (being found at 74.91.118.209:27015 at the moment) and um yeah it holds up especially for being free with Half-Life 2 and not being a massive install. Oh yeah and also the player model portraits in the Options -> Multiplayer section, love those.

half the gameplay is spawning in and getting instantly killed by either the 357, crossbow, or rpg, without any time to react and not even knowing who killed you
the other quarter is watching the desk you just threw at your enemy phase through him, and then getting instantly killed 2 seconds later. At least that is my experince on the 1 populated server that does not have 300 mods. The last quarter of gameplay is fun engagements, where when you die it feels like your fault, and if you kill someone, it does not feel like luck, this can only happen on good maps (3 of them) and/or non-laggy servers with people playing on them (I cant find any)

you play of game