Let me get this off my chest first.  I am a PC gamer at heart.  I am also a HUGE fan of the original Crysis.  I am also, believe it or not, a huge fan of the sequel.

Naturally, there are some expectations to the sequel. Namely, open world gameplay and a reason to start scouring newegg for a new PC. Crysis 2 doesn't have any of that. Crysis 2 is largely a different game that has the misfortune of having the name Crysis in the title. That isn't a bad thing. I'm sure everyone would be raving about this game if it weren't Crysis and it were instead called... uh... Nanosuit: Manhattan Virus. Instead of an open world with multiple approaches to combat, Crysis 2 opts for a different style. Crysis 2 is a linear environment with a massive number of open world opportunities. The linear presentation allows for a lot more focus to be put in individual areas, which contributes well to Crysis 2's style and tweaked combat, which I say is superior to that of the original.

Note I said style, not graphics. In Crysis 2's optimization, graphical fidelity took a hit in some of the less noticeable places, but have gained an edge up over Crysis 1 in other areas. In all, Crysis 2's graphics are different. Not better, nor worse.  ( Note too, that with Crytek's new DX11 patch that's released at the time of this writing, Crysis 2's graphics have now surpassed anything on the market, past or present, including Crysis 1.)

Storywise, Crysis 2 shines in comparison to the original Crysis. To make cinematic comparisons, Crysis 1 could be compared to a Micheal Bay film. Really d**n pretty, but not much for narrative. Crysis 2 manages to be more like a James Cameron or Chris Nolan flick. Pretty as hell, yet it manages to support worthwhile characters and plots as well. It's no Half Life, but it is one of the better FPS stories out right now.

For better or for worse, the gameplay and nanosuit features, which were the second main selling point of Crysis 1, have undergone an overhaul.  As opposed to the 4 nanosuit functions activated via a splash screen wheel, the new nanosuit 2 has 3 modes, with active cloak and active armor bound to two buttons, on the PC, "e" and "q" respectively, and a passive "power" mode that controls melee combat, sprint, power jump, and improvised projectiles (cars, people, teddy bears).  Some of the deeper features of the nanosuit 1, such as the checks and balances to fist combat and the improve accuracy in strength mode are cut in this new suit.  But the nanosuit 2 has some new tricks up it's sleeve.  By killing aliens, the player can collect "nano-catalyst" which can be used to upgrade the nanosuit to fit different play styles.  Some upgrades are your standard "fun faster/absorb more damage" fare, but other upgrades introduce special moves to combat.  One particularly enjoyable one is the air stomp ability.  With air stomp, you can lock up your armor mid-air and come crashing down to the ground with an impressive first person animation.  This impact is powerful enough to kill any foe unfortunate enough find himself inside the impact radius.    

Critics of the original Crysis cited the simple minded, unobservant, and un-aggressive nature of the enemies.  For the sequel, Crytek tried to improve the AI.  It's hard to tell if improvements were made, or if the AI took just took one step back for every step made in it's improvement.  When it works, enemies are unrelenting, intelligent ,  communicative, and impressively observant, like the AI in the first game tried to be.  Enemies would dynamically seek cover, flank, communicate my position to teammates, and then fake me out to get shots into my back.  When it doesn't work, well, it's quite pathetic.  There were semi-rare occasions where an enemy would get hooked up on an edge or start shooting at a random wall.  But with unscripted AI like in Crysis, there are almost always issues like this.  Other times, the AI would be borderline omnipresent.   A particular alien enemy, the Pinger, instinctively knows where you are, and will follow you and shoot you, even when you're cloaked.  The Pinger is a brutal enemy who can only easily be killed by shooting a classic Zelda glowing red weak spot on it's rear.  The same rear that you never get to see because it follows you around like a hawk.  

Crytek radically altered Crysis' multiplayer this time around, shifting the focus from large, battlefield type areas to smaller Call of Duty style arenas.  Crysis 2's multiplayer shamelessly borrows from Call of Duty, but offers significant improvements to the formula.  Aside from latency issues in the console versions, Crysis 2's multiplayer is much more stable than that in the Call of Duty franchise.  Glitches are few, and rarely widespread, and those more common glitches are usually isolated and fixed within a week.  The nanosuit lends itself well you the fast paced gameplay of Call of  Duty.  It just feels right.  

Ultimately, it's not safe to say that Crysis 2 is better or worse than Crysis 1.  It's different.  And its really good.