My problems with the Ranger class break down in 4 areas:
1) TWF and Ambidexterity. Yes, everyone brings this up... because it's obvious. It's also very very easy to fix. Personally, I'd give rangers, oh, a bonus feat at levels 1-3 from a list including TWF, Ambidexterity, Track, and some bow feats. There, fixed.

I almost don't rate this as a problem, because it's so easy to fix... but it's still there.
2) Favored Enemy. My problem is not that this is DM fiat... after all, turning undead and sneak attack are both vulnerable to DM choices, to name two obvious oens. The problem is that it is _very_ DM fiat.
See, turning undead... well, undead are really really common. A lot of monsters, spells, and adventures deal with undead. So at least there's a good chance they're going to come up. And you can design clerics that turn/rebuke other things, like plants and elementals. (Via domains) Hmm. There's a thought... allow clerics to take a domain-like turn in the place of turn undead... oh, getting sidetracked.
Sneak attack... well, roughly 1/3-1/2 of the monsters are invulnerable to this. Which is annoying... but in the end, shouldn't be insurmountable. Unless the DM has the 'all undead' campaign.
But favored enemy is _very specific_. It's one of 20 or so types.
This isn't bad merely because the DM might 'screw with you,' but because it sets up antagonism. As a DM, I have to worry about 'sheesh, should I toss in more goblins in this scenario?' I'd rather not have to worry about them.
I'd be happier with fewer favored enemy choices, maybe broad things like Humanoids (goblins, humans, elves, ...), Animals, Elementals, Fey, Plants, ... something with 5 or so choices, so without trying it's likely the DM will include them.
3) Overall focus. Actually... this isn't a problem with the class as written, unless you count 'it's not made clear enough.' The ranger is a class about, well, ranging. Being a scout. Mucking about in the woods and tracking things. This should be rather obvious...
The problem, however, is that the character is again sensitive to DM choices, bringing up the antagonism again. If the DM has to include woodland elements just to make the ranger have something to do, this can also create a tension with the other players, who sit around bitching while the ranger strides happily through the woods.
Rogues, with the use of sneak attack, are quite useful in melee and ranged combat (depending), but have a variety of cool other skills and tropes. So they aren't limited the same way into just doing 'roguey things.' However... locks, traps, and treasure are something clear to the focus of D&D. Unlike rangers, people are more likely to be interested in the rogue's core focus.
This isn't a problem with the class perse... I mean, how else would you design a _ranger_? But it's a problem of presentation. It would be nice if there were more material showing how to integrate woodland elements into campaigns... though I suppose that's the job of world books and adventures.
4) Magic. This is another 'problem in Will's head' rather than a true problem. Personally, I hate that rangers have magic. Just rubs me the wrong way... I realize others disagree, but I'd like to see rangers as a cool skilled fighter/scout type, occupying a niche distinct from both fighters and rogues. Need magic? Multiclassing as druids or clerics works perfectly fine.
But that's me.
Luckily, there are resources to design your own classes.

My favorite is:
http://www.custoscogitatum.com/classcalc.cfm