I would like to hear someone's opinion who never heard them before. Maybe Kade can "A/B" it assuming he doesn't know the original.
Having heard a few F&J albums, but not those, I gave a quick listen to a few of the same songs from each. Personally I kind of prefer the newer production a bit. The original guitars sound a little farty, and there's not much bass in the mix. I wouldn't call the newer mix amazing, but it improves on those two aspects, the guitars have more bite to me.
There are two things that I think bug people about the rerecordings. One is the vocals. He definitely doesn't have the youthful enthusiasm, and doesn't bother even trying to hit some of the high notes of the originals. The other is that the tempos are definitely slower on a number of the songs. That's probably where the feeling of lower energy is coming from. I don't have the familiarity with the originals to have those ingrained, and the "correct" tempo for a song is kind of subjective, it's possible they were too fast on the original (though probably unlikely for thrash crowds), but I can see that being a major hangup for many.
On the other side, Chris Poland guests on three tracks on the newer version, that's hard to beat.