The first one scared the shit out of me when I first saw it. I'd say T1 was the better of the two when it came to the scare-factor but T2 was an all-round entertainer. Robert Patrick's icy demeanour and fast running put the shits up me, too. Plus, with his liquid metal weapons he was completely creepy. It had the machine learning to be human angle, some memorable lines and some good bits of humour, too.
T3 was... urgh. It was almost like watching a parody. It was like the people behind it were so scared of going up against the previous films' reputations that they just didn't try to do something comparable. Way too much in the way of humour and gimmicks. The 'Terminatrix' was one big gimmick with a load of crap lines -- do us a favour, love, Mr. Patrick already has the 'look scary and run fast' market cornered. The acting & characters were also hammy. John was a whiny little bitch and Katherine was a predictable nu-woman with bigger balls than John. It was just irritating to watch plus, as D3ads pointed out, they fucked up the entire plot, even if the final twist was unexpected. The action scenes were good (especially the crane chase), but that was about all I can say in its favour.