My first impression was that the first one felt more "finished", more polished and superior as a standalone work of art, but the second one is more ambitious, stretching farther and bigger. Metaphorically speaking, right now they are mid-air, halfway through an absurd 720 degree twisted rotating gymnastic (artistic) maneuver. I suspect that how I eventually feel about Across is going to depend on how well they stick the landing (in the third installment).
But I do need to see it a couple more times to absorb everything they did in it, to be fair. I think I saw Into in the theater three times and have watched it a couple of times at home since then.