Alicization and War of Underworld combined is the best out of SAO IMO. It was confusing at first in episode 1, felt super cheesy and almost skipped it but I'm glad I didn't. It is not a prequel, it's just setting some background information for the rest of the show moving forward. Probably the best season of SAO out of all with 0 filler episodes unlike SAO 1 and 2 where Aincrad felt super filler. Just push through episode 1 and I'll guarantee you the rest of the series is worth watching. Honestly a shame they made the villain super hot LMAO!