Before I go into (short) detail about the two games separately I'll tell you my general feeling of them. I love the story based things. Like the first few test chambers in the first game which gives you a feel of Aperture, and then the ones in the end where GLaDOS turns on you, and the final battle. In Portal 2 they are the beginning when you wake up after being asleep for a reeaaally long time, then when you get GLaDOS back online, when Wheatley finally starts the escape, when Wheatley becomes corrupted, when GLaDOS is made into a potato battery... You get it... The funny things that are part of the story. But the test chambers in-between those moments just feel like fillers to me, and they got repetitive. Sure, I died a lot, and several times I had no clue what to do, so it's not like I just breezed through any of the games and was bored by the tests. They just became too many, you know? And not with enough variation to remain interesting. They just became a hurdle to get over so I could get to the next interesting part - the story.
The first Portal was very linear and between the original introduction and the point when GLaDOS tries to kill you in the incinerator nothing much happens. You do the tests and listen to GLaDOS's sarcastic humor and mean comments, the further you get the meaner she gets and it got pretty obvious waaaaaay before the revelation that she was the bad guy, and then it was just doing-as-you-were-told and waiting-for-something-to-happen. Except for feeling very bad about it when I dropped a companion cube into the incinerator after GLaDOS instructed me to, nothing memorable really happened before Escape time. The boss fight was cool, though. The ending scene had me really confused at first, because when you see the player character being dragged away and hearing the mechanical sounds I thought that my character had been an android or something all along and that the mechanical sounds was herself dragging her away from the explosion. It wasn't until I started Portal 2 that I realised that she had actually been dragged away by a robot and put back into Aperture.