BiggusGeekus said:
First, rangers are great: http://www.murchadslegacy.com/rantranger.htm The problem is that when you play a ranger like a fighter the ranger doesn't come off as well. Much in the same way if you play a druid like a cleric or a barbarian like a wizard. The second problem is that people focus on damage per round. Rangers do other things that don't involve doing damge. So if you ignore those things it looks like they can't do much.
Also, I'm a beta tester for NWN. I'm still bound by the NDA, but I can tell you that there is nothing wrong AT ALL with the ranger.
BiggusGeekus is right on all points, and does a good job of summing up why the ranger is a viable class in D&D 3rd edition.
However, you're right to notice that there has been a lot of disappointment in the 3rd edition ranger, and not just to the average DM or player. Notable game designers like Monte Cook have also expressed concerns about the class, and several "alternate rangers" exist to "fix the problem". The things that people don't like about the 3rd edition ranger include:
1. The class seems front-loaded. There is a lot of incentive to take just one level of it, and 3rd edition's improved multiclassing rules encourage this.
2. The ranger's favored enemies abilities sometimes don't come into play. If the DM doesn't challenge the ranger with their favored enemy, then it's a useless ability, unlike something along the lines of the barbarian's rage that can always be used.
3. Some people dislike certain class abilities because of the flavor of those abilities. Many see Two-Weapon Fighting and the casting of divine spells as illogical abilities for a wilderness warrior class.
4. A few think that the ranger should have been a prestige class.
Note that I'm not really on either side of the issue, just playing devil's advocate. My opinion is that rangers are ok, but could be improved in future editions by giving them better abilities at levels 2 through 20, and possibly getting rid of the spellcasting.