I still have lots of fun with it, but it's just not the same (wall o' text rant inbound!)
Yes, there's still a community of sorts. The player base skyrocketed after the F2P update and has consistently stayed at high levels, so you never have to worry about finding a populated server. The downside to all this is that the community has lost its "soul."
A few years ago Valve started pushing official servers via the "Quickplay" option. While it made jumping into a pub game extremely simple, it had the unfortunate side effect of killing off community servers. It's always a random group of people whenever you join a pub game now, not a tight-knit bunch of "regulars" that would frequent particular servers. I'm afraid the likes of this will never be seen again:
Now hardly anyone uses their mic, and when they do it's usually to fling insults at one another. It's definitely a more caustic environment than it used to be.
Another aspect to consider is the skill level disparity. Since everyone goes to Quickplay servers now it's always a crapshoot whether the matches will actually be decent. You've got longtime veterans with thousands of hours under their belt matched with total newbies and young children. This results more often than not in absurdly mismatched games, where a small group of pubstompers will band together and absolutely annihilate the other team. Valve keeps talking about introducing competitive matchmaking, but until that day arrives you have to go in expecting a steamroll one way or the other.
There was the issue of rampant idling/begging/scamming on official servers, but that hasn't been much of an issue lately ever since Valve introduced a bunch more hoops to jump through for trading, including verification via smartphone.
Finally, the switch to F2P has attracted the attention of hackers. After all, why worry about a VAC ban when you can create an alternate account and start playing again within minutes? A particularly nasty variety are those that use a program called LMAOBox, as it's apparently extremely hard for VAC to detect. Hackers don't crop up all that often, but it certainly happens far more than in the early days (I ran across maybe two hackers total from 2007-2010. Now I run across one every few play sessions).
As for the campaigns, they're similar to the contracts in CS:GO. Every few days you get a few tasks to do (score a certain number of kills, cap the point "x" number of times, etc.), and when you finish it you get either a random painted weapon or a special crate that has a chance of giving you a higher quality random painted weapon. You usually have to fork over some money to participate though, usually around the $5 mark. As for me, I don't bother because:
1. I find most of the weapon skins to be ugly as hell and clash with TF2's original art style (as if all those garish hats and particle effects weren't enough).
2. They cause my frame rate to drop like a mofo.
That's something else to consider as well. There have been so many additions and changes slapped on top of the game's original code that it's now creaking under its own weight. When I first got TF2 I could run it on high settings at 30 fps or more. Nowadays I have to run the game on the lowest settings in DX8 mode with a special "no hats" mod to remove most of the cosmetics and unusual effects...and it struggles to maintain 30 fps, often plunging into 20 or under in large firefights. Granted I have a toaster of a computer (2 GB RAM, baby!), but it should still easily be able to handle TF2's listed system requirements. Indeed, I recently downloaded a stand-alone mod called Team Fortress 2 Classic that, among other things, reverts much of the game back to its original 2007 state. What a difference! The mod runs smooth as silk, whereas TF2 proper is slowly shaking itself apart. Valve has indicated that they're going to work on optimizing the game for competitive matchmaking, but I'll believe it when I see it.
TL;DR - TF2 is still a fun game, but it suffers now from a toxic community, visual garbage and code held together with bubble gum and spit.