Great: Picard - Patrick Stewart was superb in it, most notably his post assimilation spell at home, and his torture at the hands of the Cardassians. I can't imagine any of the other actors pulling those off.
Oh and the Nebula Class
Good: The Galaxy Class. Oh in hindsight I can see its faults, but when I first saw the series I thought the ship was fantastic. Big, great bar, and nicely decorated.
And I still think it has a great shape - though I liked it better when Admiral Riker - probably in the midst of a midlife crisis, had an extra warp engine and a really big gun fitted.
Average: Geordis visor. Was probably budgetary restraints, but I'd like to have seen a little of the world through his visor. I still can't understand why it seemed to send so much information at once, leaving Geordies poor brain to filter everything out. Couldn't the visor itself just trasmit normal images, and switch to infrared, night vision, and Pan and Zoom when he needed it.
It also allowed him to be brainwashed, sent Worf zipping through parallel dimensions, and then got the Enterprise destroyed.
Bad: Wesley - he didn't have to be such an annoying character. Jake and Nog developed from annoying tikes to fully rounded adults - Nog being the one who joined Starfleet and Jake going his own way made it all the better.
Wes should have been a bit more of the Genius and a bit less of the adolescent. Maybe then his presence on the Bridge and in conferences would have seemed a bit more acceptable.
Terrible: The Ferengi. So much so I was dreading them appearing in DS9, but Quark, then later Rom and Nog, really did the species justice.
In TNG they were too cartoon like, I could never imagine them ever joining Starfleet.