I like portal 1 quite a bit more than portal 2. Portal 1 felt like this dark mystery with occasional bits of humor. It felt very connected to Half Life, not necessarily in story, but definitely in atmosphere. Portal 2 was missing a lot of that. It oddly felt less lonely than Portal 1, and was missing a lot of that Half Life atmosphere.

Additionally I love the implications that Portal 1 has if you play Half Life. Outside is absolute hell, and you don't know if you'd rather be outside the facility or inside it.