If you're looking for a comedy, Pineapple Express delivers big time. What I had a hard time with was the action and in my opinion if you're gonna make an "action comedy" there should be an equal amount of action and comedy. The movie was hysterrically funny and action packed, but the action wasn't as actiony as I would have liked it to be...
How do I explain this? I guess I prefer a funny action movie over a comedy with a lot of action. True Lies, Lethal Weapon, Indiana Jones (1, 2, and 3. Not 4), Pirates of the Caribbean, and Die Hard were all action movies that were funny. Pineapple Express is a comedy at heart with a lot of action. The action sequences weren't serious enough, maybe? But in some cases they were almost too serious, like they were mocking themselves, but not doing a very good job.
Seth Rogen continues his reign as best average Joe in a movie, and James Franco shows a side that I had never seen before. Rosie Perez returns to the big screen (in wide release) for the first time since Riding in Cars with Boys... which I haven't seen. She shouldn't have come back. I think she may be one of the main reasons that the action sequences weren't done very well... she was in them.
Alternatives to Pineapple Express: Hot Fuzz, Shaun of the Dead, and Superbad.