I've been playing since early beta and I'm still having just as much fun with it now that I had when I first started. There is a ton of customization and variety when it comes to your character, and a little planning can go a long way.
Its the game I've been waiting for all year, the one that makes me look at the clock and do a double take because 6 hours have passed in the blink of an eye. Most of the releases this year have been somewhat of a let down for me, but this game has the potential to be one of the great time wasters .
I like the crafting and item recycling, sometimes I pop back into town just to see if they have a mod list up (I pump everything with electricity and toxic)...and its nice that the craftable items increase in power as your standing goes up. I've even made a couple of uniques that I traded for some mods that I needed, and/or sold for a tidy profit.
The hellrifts, bloodgates, and passageways are nice additions, and even if I don't get a rare spawn/chest I'll still get the increased XP for fighting inside of one.
The enemies are varied and interesting (love the design work on spectrals) and once you hit act 4 they really start to ramp up on density/danger level. The giant lumbering baddies are also always fun to kill, just don't let them hit you .
So far I've gotten my marksman up to 27, and it has been fun planning what build I want to go with, and discussing the various skills with other MM (I personally don't like the idea of respecs, but agree that there should be a penalty and the option to do so.) I think the tree was designed well, and has a decent amount of flexibility to customize without risk of being rendered useless (if you are careful and have a clear goal).
Also a couple tips for newcomers to the hunter clan: Pick a strike and plan to invest in it (I use smackdown), the damage scales based on character level and you will come to swear by it. If you're going to make a first strike, it may as well be one that drops all enemy shields and stuns, ignites, or silences targets in the strike radius.
If you want to use grenades, go for phase and invest in it, phase is one of the best debuffs (50% increase in damage taken, 50% decrease in damage dealt) you can apply and will save your life on occasion. Plus being able to drop a phase and beacon then whip out your sniper pistols and go into sniper stance for an instant kill on all but the toughest bosses never gets old.
Everyone has already listed the faults, but in my experience since early beta, the developers have been quick to fix major issues that have cropped up. And ping0 has been great at communicating what is going on (even announcing in game for important notices), and I really hope they get the support needed to continue creating/updating/fixing things. The only issues I have is the memory usage, and the speed of the interface, but hopefully that will be resolved with the patch that goes/went live today, anyone have it applied yet?
All in all I've had a lot of fun playing this game and I look forward to future content. If you're on the fence I would say check back in a month or two, if you liked D2 and don't mind a few annoying issues, you might just lose large chunks of time in the fight for the living.