So, I've got about almost 7 hours put into L4D2 PC - these past two days. Namely, first two Campaigns of L4D2 - Dead Center and Dark Carnival. Dead Center has 4 parts to it, while Dark Carnival has 5 parts to it. I ain't played the other 3 campaign yet - so, no comment on those last 3...yet.
Here's what it comes down to - if you liked L4D1, you'll obviously like this. How can you not, honestly? It's basically more of the same - but done w/ better in execution. Not much in the gameplay department has really changed. It's just Valve decided to throw in more of everything - few new enemies, few new gun-weapons, melee weapons, new MP game-mode, and the 5 new campaigns.
Best thing to happen to L4D2 is melee weapons. I really did wish Borderlands had these - namely for Brick, since he's more or less a melee expert (with his fists) - but yeah, melee weapons in L4D2 rock. The melee weapons in L4D2 are awesome for battles hordes - which since to come in flocks quite often. Axes, guitars, baseball bats, cricket bats, - and especially the chainsaw - if they are coming at you, your best bet is often to switch to melee and go nuts. Prepare to mow 'em down.
Speaking of hordes, this leads me to my next point - difficulty. L4D2 really feels like it was made for veteran players of L4D1. In L4D1, Normal felt like a good place to start for gamers - while, I don't think the same can be said for L4D2. L4D2 on Normal Difficulty feels like L4D1 did on Advanced - hell, maybe even tougher. On Normal in L4D2, you WILL need to push back enemies and then shoot/swing OFTEN - which was basically necessary to survive in L4D1 on Advanced. It was tough enuff w/ The Smoker being able to make you unable to really do anything until a teammate helps - but toss in the fact now you got new enemies like The Charger and Jockey - it gets even harder b/c they render you useless w/ one special attack. You're even more so in for a challenge b/c these enemies hit you with their special attack, if nobody helps you, you're screwed no matter how much health you have - b/c a teammate must help you so you can get free. The Spitter just can do acid damage on you, basically - and you step on its acid puddles, expect to get burned for some damage.
The defibrillator item feels very necessary b/c you and your teammates WILL get knocked down and will eventually die. Expect to get knocked down OFTEN. And the AI Director really feels like it always wants to throw the kitchen sink at you - even on Normal. I ain't tried Easy here in L4D2, so...I dunno' how hard or easy it really is or isn't.
From what I've played, L4D2 is definitely an improvement on L4D1. L4D2 is obviously the better game here and packs more content right in the box and all. One thing the original L4D1 had is missing this time around in L4D2 - the fresh feeling of playing something brand new that really made the first game so great (despite its short length and lack of content). A lot of the formula, style, structure, and whatnot you found in L4D1 is also here in L4D2 - even if there's a few very small minor little tweaks and changes to it. Also, I really do wish they could've found some way to improve the storytelling aspect in this game w/out the expense of sacrificing any of the gameplay of course - even though the stories all do connect here, it doesn't feel like much was changed here w/ making the story anything spectacular as there's not a hell of a lot really to it here.
Is L4D2 worth my $30? So far, it sure feels like its worth (stand-alone) expansion-pack pricing. I'm still having a blast and a lot of zombie-killing fun, regardless.