My only problem with the game is the constant need to upgrade equiment when you probably don't have the crystals or the money to do so. It became even worse at the end of my playthrough when I'm guessing you updated the game to automatically refresh rare items inthe store. It only meant that an item that I liked was going to be too expensive and it would disappear by the time I had the money to pay for it. Waiting to craft with 10 crystals is a must given how much better a rare or legedary weapon is. Upgrading items is virtually worthless because you'll be trading it for another shorly after. Therefore you shouldn't have upgrading in the game I don't fault you for using in game purchases, but I wouldn't want to buy something so short term.
I never had to grind because I could dodge the bullets pretty well and the items I found or bought could usually, even if just barely, get me through the levels. I did notice the difficulty increase, but I was able to get through the levels with 100% on most tries. The second round of bosses was just a waste of time. They were the same but with more health or a slightly different attack pattern.
I did finish the game and I enjoyed my time here. Just the things I mentioned above ruined some of the experience. I didn't play multiplayer and I have no intention to either. You should have let us use our newground accounts because it would have been easier for us.