I'm playing it and it seems like a good port, but it looks much worse in HD than the original 2D art imho. It's not a very good fit for iPhone too, since it's a lot of just tapping the screen to get to the next line of dialog, and holding the phone horizontally for long stretches of time is a pain. I imagine it's a much better fit on iPad.
You can play it holding the phone vertically too, which is what I do a lot of the time since it's much more comfortable.
It's a fine port. Some purists prefer the DS versions because they have a problem with how a few of the characters look, but for 99% of people the lower price, mostly better visuals, and convenience of the iOS ports make them the better choice for someone just getting into the series.
I will say that for some reason the 5th case in the first game, which was added when the game was ported to DS from GBA, is for some reason a little jacked up. It has spelling errors all over the place, a few weird oversights where other characters will move their mouths when Phoenix is talking, dialogue will repeat, and other annoying things. Also, one scene near the end that uses the touch screen is glitched, and I had to do it correctly about five time before it let me progress.
All that said, in my opinion the annoyances aren't bad enough to warrant paying several times more for the series, having to play it in low resolution, and not having the convenience of having it on your phone/ tablet. I think I'm a pretty big fan of the series, I've played every game (the iOS port was the fourth time I played through the first game) and IMO iOS port is a no-brainer.