The gameplay loop is pretty faithful to the original as far as I remember (it's been a few years). I did notice a few differences compared to the Untold version of 1 which threw me for a loop (they added a "hint" system in Etrian Odyssey Untold to give you an audio cue that there is a hidden passageway nearby, which is absent in this version and the original DS version).

The map controls are a bit awkward and unintuitive for me, at least so far. I imagine they're more intuitive on PC with a mouse, but it's not that big a deal.

As far as how it's aged: the only thing which really makes it feel a bit aged to me is the rather high random encounter rate. If you're used to more recent dungeon crawlers like this, they have fewer, more meaningful encounters on average; the EO series has a lot of simpler encounters that are there to drain your resources, and to make it a bit of a gamble about whether you can avoid the FOE who's chasing you. It's not bad, but it's something to consider.