I'm a fan but I've found some of his later stuff to come across as his going through the motions to the extent that I haven't even checked out the last three (which includes the two you mention by name).
Generation X is a his first and a one everyone has heard of and it's certainly worth checking out, in my view, but I don't think it's his best.
I love Waiting for God which is a short collection of vaguely connected short stories which you could read in a couple of hours. A good introduction without because of its brevity but also, not quite like anything else I've read of his.
Shampoo Planet has that difficult sophomore album feel about it, if you get what I mean, but I still liked it.
Girlfriend in a Coma is a good one with an interesting premise.
Miss Wyoming is pretty daft. (I think) it's meant to satirise B-Movies / TV soaps by having a B-Movie / TV soap actress living a life that imitates art but it just really reads like a corny soap / B-movie in the end. All Families Are Psychotic is about a dysfunctional family and is pretty much 'classic Coupland' with its many pop-culture references and so on. If you like his stuff,
you'll probably love it. Hey Nostradamus! Is about a high school shooting and inspired by the Columbine shootings. Again, it's classic Coupland. Eleanor Rigby is probably my favourite novel of his and it actually made me quite, which is not something many books do and I think it's an example of where Coupland transcends his usual themes of pop culture / zeitgeist / whatever and shows great empathy for the main character (Liz, a woman who had a child after losing her virginity of a school trip and then has the kid adopted - any more details would spoil it a bit). J-Pod and The Gum Thief are easy reads (all Coupland's books seem to contain prose which takes little effort to read, which is part of his charm in my view) but they're both a bit 'meh'.
I've got one of the early paperback editions in that large format with the messages in the margins. I'm not sure if the later editions have that but a lot of the ones I've seen in bookshops are just normal sized ones though so, even if they do have them, I don't think it would work as well. I think that, even if you don't like it, the format was something different at least. I found the characters a bit lame though. And I'm a bit of a slacker myself.