Well the one thing I don't agree with is splitting the game in multiple parts for Steam... I AM planning on buying it on Steam, but not before it is FULLY finished (because I'm not taking any chances of buying unfinished games, even though I believe they will finish it). Let's hope not everyone feels the way I do or it won't sell that much (but usually it works for devs to split their games this way, so hopefully it'll be fine).
That said, if that's the way they've decided to do it, so be it, it's not my or our decision... and that said, if they've decided to release it in parts, then YES, it's absolutely essential that they re-do the 1st part ASAP, because as it is, it will NOT get good reviews, the begining of the game is pretty rough right now.
My point being: while I don't necessarily love that decision, I do think it's better to focus on polishing what they've decided to release on Steam first, makes the most sense.