I have played OOTP from the very first version, and played iOOTP and then MLBM from the start as well, so my observations on this new mobile game are naturally shaped by this past experience. I have only played a few Go! games all the way through and simmed 25 years or so of a fictional league, but have some initial reactions.
The depth of the game is impressive; obviously, so much more here than with MLBM (but then this is what you would expect since it is the same engine as OOTP desktop). But the level of detail wrt features, options and the like seems mostly devoted to franchise and league-level play ... including the creation of alternate baseball universes (although the mods you can use with the desktop game, and the often wonderful rabbit holes you can end up going down -- thinking of uniform design in particular! -- nevertheless make the alternate universes in Go! less customizable).
Yet I very much like to play individual games (even in replays, trying to keep up the pace in terms of that particular MLB season, day to day) and here is where my biggest disappointment lies (maybe really my only significant disappointment): No pitch-by-pitch mode! I remember well how thrilled I was when Pursue the Pennant came out with the first serious (and realistic) pitch-level sim, after some three decades of batter-level board and computer games (yes, the designers of Earl Weaver, God bless them, put this in their game, but it was not clear how realistic it was in terms of being based on real life data). And this having pitch-by-pitch is what made me eventually devote more time to OOTP than PTP/Diamond Mind even for season replays (of course, the universe-creation opportunities in OOTP made it my choice from the start for everything but single season replays).
And then the fact that iOOTP/MLBM had a pitch-by-pitch mode option was what made the mobile game so much fun for me: I could create a fictional baseball universe, play the deadball-style game if I wanted, do pitch-by-pitch management of my own team's games AND do all this right on my iPhone as I rode on the BART
Plainly, if I had one ask for you, it would be to please please please add pitch-by-pitch.
A bit more on customizing Go! ... As I said, you can certainly do a lot here but it would be great to have some detailed guidance on it all. But I assume eventually there will be a manual -- honestly, I have spent a lot of hours over the years pouring over the OOTP manual(s), and have always found it extremely helpful in navigating through what can feel like a maze at times.
There has been feedback from some folks on being able to save a game and then return to it later. I have to concur, especially as I like to play individual games and when you realize you have to break way for some real life stuff but have not yet finished the game you are in, it can be frustrating. If you prefer to do sims of seasons, this will not really be a problem, but again, some of us like to play through entire games ... and do it pitch by pitch
-- so....
But enough of this -- all in all, OOTP Go! has been really fantastic for me so far; I am already devoting too many hours of my day and night (or so my wife ever so gently informs me) to playing it. Well done!