I've got a few:
Seattle Short. Let's take everything that made the full Seattle great (the bumps, elevation change, fast corners, etc) and get rid of it. Now it's just a boring, less than average street course!
Tahiti Road was also pretty bad. Requires no skill and is a chore to drive. Same with Seoul Central.
Err..those tracks are in GT2. This is a GT1 forum. Good points though, I never really liked Short versions of courses (Seattle, Rome, etc), they always feel butchered and lacking. It's good for earlier races though, when you only have 60 hp on your Kei car and the top speed is only 50 mph

. At least you won't get asleep driving on the long straights

.
Tahiti Road is an okay course actually, there's some fast and slow sections. Couple of 90 degree corners, elevations changes, and turn 3/4 IIRC is like a mini Eau Rouge. The last corner also requires some guts to take flat-out, as you can smack into the pit divider if you're just a tad too fast. The thing that lets this circuit down though, is the graphics. I am 100% sure PD spends the least amount of time modelling this circuit. It's way too pixellated, even for PS1 standards

. Otherwise I think it's a fine circuit.
No comment on Seoul as I've never played GT4.
But by far my least favorite track in a GT game is Tsukuba Circuit. I know there are some out there who really, really like it but I just can't see why. It's repetitive, it's in a ton of games, and I'm tired of driving it.
Again, this track is not in GT1, but I can give you a reason why quite a lot of people like it. Tsukuba is the TOP Time Trial circuit in Japan. Especially for JGTC and JDM/Tuned cars. It's sort of like the Japanese version of Nordschleife (not for length, but for popularity and status as a TT circuit). So I can understand why many people like to drive on it, whether it is to test cars or just to compare their laptimes with real world laptimes. I haven't driven this circuit personally, and from the track map I must say it looks pretty boring. But I'm not counting it out yet.
On a seperate note I really loved the stadium atmosphere of the old High Speed Ring in GT1 and GT2. Not a fan of the resurrected version in GT4 and GT5P. Same thing with Route 11. The original with the underground tunnel section is better than the GT3 version in my opinion.
Hell yes! Another lover of the old HSR & SSR11


. I really hate the new HSR in GT5P, it's more beautiful and looks more professional, but HSR isn't supposed to be a top-tier circuit. It's like a high speed go-kart track for normal cars. That said, I doubt the old HSR will suit GT5P/GT5's physics well (banks too steep, kerbs too high, etc). I hope it comes back as a separate version though, HSR - Classic & HSR - Modern

.
As for SSR11, it's the best fictional track EVER (and yes, I mean the GT1 version, not the unchicaned GT3 version). Heaven knows why PD decides to scrap it.