Season 1
One of the best seasons of TV ever, hands down.
Season 2
I'm one of the few people who liked season 2 nearly as much as 1, but I understand why most felt its structure was too needlessly complicated. That said, the season 2 finale is one of my favorite episodes of television ever, more so than any individual season 1 episode.
Season 3
The first half of the season was some of the best sci-fi I've ever seen. Second half was WAY too rushed, though, even though I liked the basic story that was being told. A big part of the disconnect, unfortunately, was cutting the season down to 8 episodes from the 10 of the previous two seasons, yet trying to establish such a massive world and tell such a massive story in that contracted amount of time.
Season 4
Same as season 3, the first half of the season was great, to the point where we and every other site were excitedly claiming Westworld was back. However, then, also like season 3 - but even more so this go around - the second half of the season took a massive nosedive, killing off beloved characters in some of the most random and uneventful ways, limping across the finish line in such an utterly an disappointing manner.