Still Going Strong!
First off, the single player campaign is short but still enjoyable with one or two key moments that are quite memorable. Ratching up the difficulty to Veteran extends the appeal by some distance, and there's a fair bit of replay value across the difficulty settings (as well as all the achievements to rack up as well).
The multiplayer is standing the test of time, as you would expect for any game from this franchise. The matchmaking system is reasonably good, but every once in a while you will find a fairly new player in amongst a bunch of prestige players getting it handed to them. I guess the problem is that most people who are interested in playing this game have got it by now, and I reckon that the supply of noobs will gradually dry up over time. There's a definited hard core element playing which can make it frustrating.
The only criticisms I would have of the multiplayer is that the grenade launchers are overpowered and too easy to use.