Hey there,
I m getting close to the end of Gothic 1. I personally didn't enjoy a rpg game like that since Torment. But anyway, according to most comments Gothic 2 seems to be almost as good, so I m not worried about buying it.
On the other hand rpg gamers are unanimously saying that Gothic 3 is not as good as the other Gothic games without really explaining why. What makes Gothic 3 so inferior ?

First, keep in mind that Gothic 3 isn't a horrible game by any means. Just not nearly as great as it's predecessors. So what makes it fall short of the previous games greatness? Well...here goes...
First, the world feels to "stretched thin", for lack of a better word. Both G1 & 2 only featured a couple of towns set amongst a rather smallish countryside. I don't consider that a bad thing, considering that both those games had far more detailed and believable worlds because they had such tight focus. With G3, Piranha Bytes figured they could keep the same level of detail in all their towns and surroundings, but expand the game world to Oblivion proportions..and...eh...they didn't quite succeed. The NPCs in most of the cities felt one dimensional in comparison to G1 & 2, and the countryside worked more as a pretty backdrop than an interesting place to explore.
That isn't saying the game is devoid of any of the magic that made the previous Gothics so much fun. It's still there, but more as an occasional thing that a constant companion.
Beyond that, you got the combat. This is the one thing I can say sucks the most about the game. The neat left swing/right swing/lunge/block system is gone, replaced by this CLICK THE MOUSE AS FAST AS YOU CAN HIT IT HIT IT HIT IT DIE EVERYTHING DIE setup that makes the game way, way, way too easy. I mean seriously, you can beat the everliving hell out of every human opponent in the game at level 1. No challenge whatsoever (boars withstanding). For those of us that actually preferred the get kicked in the dick difficulty of the first two games, this was practically a deal breaker.
Then you've got what they did with Lee. That's some tragedy right there. And not the good greek play poetic tragedy here, rather the "what the hell were they thinking" kind.
So in closing, it isn't like Piranha Bytes woke up one day and decided to suck, but I would say that PB stretched themselves too thin on such an ambitious project, and the whole game suffered for it. Still, despite the flaws and my big complaints, G3 is a goodish game when it comes down to it, and worth getting if you're short on other RPGs to play in the meantime.

Thx Renzatic. I'm satisfied with your detailed explanation. I now understand better the difference between G3 and G1-G2.

You should definitely play Gothic II next regardless; its ending leads directly on to the events of Gothic 3 and things will make a lot more sense if you play them in order.

I wasn't going to skip Gothic 2. That wouldn't make any sense :)

Also, JoWooD was accused of rushing this game at the time, which means that it was probably meant to me much more developed (and less buggy). Since then, Piranha Bytes had severed ties with JoWooD.

Yes, Piranha Bytes has washed their hands of the whole business; Arcania: A Gothic Tale (Gothic 4) is not by Piranha Bytes, nor is the dreadful standalone expansion Gothic 3: Forsaken Gods. Piranha Bytes is now working with publisher Deep Silver on a spiritual successor to Gothic called Risen.

gothic 3 was also buggy as hell on release, like unplayable bad. the new community patches that have come out make it actually just fine, except for some light effects still slow down my comp like a mofo... a lot of the reasons it got bad reviews were the bugs, which have mostly been fixed now

Flawed though it is, G3 is still better than Oblivion.

having just beaten Gothic 3, I can also say that the ending is horrible.
***spoiler
you play throughout the entire game, going through the different towns and completing their sub-quests and gathering some items, until you get to the point where you have to choose which side you're going to support. I figured at this point you'd end up in some final dungeon/area where some kind of climactic showdown would take place, so I pick a side and kill the other people who I didn't pick, then follow Zardas to the 'portal' he speaks of which ends up being a blank rock wall on a cliff that I click on and the game ends. WTF?!?!?!?

I agree. The fights to kill the two leaders were just long and dull and the last enemies you encounter on the way to the portal didn't even stand a chance. Though by that time, I was tired of the game and just wanted to complete it. Going beyond level 60 is pointless. The community patch does make the beginning of the game better though. It's when you start being able to slaughter herds of enemies is when the game goes downhill.

What bothered me in Gothic 3 were the pointless quests. Too many: kill 5 wolves and the dialogues were pretty thin. The general atmosphere was still there, especially in the cities and I thought Nordmar was great but they could've done so much more.
I suggest you play it but overall it's a bit dissapointing compared to Gothic 2 NOTR.

When Playing Gothic 3 keep in mind that the latest Community Patch is pretty much a must. The reason is still pretty argued about, but the fact is Piranha Bytes left the game unfinished and full of bugs. Still, the game is nearly as good as the previous games. It is very different in terms of story, world and scope but it is still a very good game.

Yeah, the Community Patch is a must. For reference you can get it right here on the Community Patch Team's website (it seems nobody linked to this before in this thread, so I might as well be the first).
Those wanting to see what a realised Gothic 3 might have been like should check out Risen, Piranha Bytes' latest game. It's set in a new universe, but other than that all aspects of it draw heavily on the mood and gameplay of the Gothic games. It has what is arguably the best combat of any of their games to date.