This series has managed to plough its own weird niche where absolutely anything goes, and this seems to take things about as far as they possibly can. There's just so much scattershot mayhem thrown in and to say too much would spoil some of the surprises and gags. All-out comedy isn't something a lot of games have nailed for me, but in SRIV the laughs come regular and loud in a way I haven't really found in other games. As a franchise it gets a lot of stick for being 'dumb' but the way it spoofs videogame conventions is really sharp and the writing in general is way wittier than most give it credit for.
It is a bit like the movie Airplane in they way it throws a ton of gags and ideas at you hoping for a high hit rate, and more often than not it works, although in places it can feel a bit random and uncohesive. I did find that it lost its momentum a few times, given the publisher woes they went through its a miracle a game came out at all but it's hard to avoid the fact that it does feel artificially padded out and repetitious in places with the same objectives popping up or assets and locations being reused (and while 4th wall jokes about that very thing are all well and good, it doesn't really help to know they were aware of it). I found the side missions in particular a bit of a chore this time round, and that's coming from someone who 100%ed The Third and never flagged.
As far as the main quest line goes though it's more killer than filler so a very enjoyable playthrough. Hard to see where they could take it from here, and I think I'd be feeling some major burnout if V appeared in the next couple of years, but as the climax to a series that just got more and more mental as it went on this would be a fitting end point.