Haven't had time to do much more than look over things since I worked all day.
Imported league from v12 and everything looks great. All of my settings seem to have come in as they were in v12.
Game looks great, player history with tabs to sort is awesome. Whole gui is very well done. I really liked the gui in v12 and before and didn't think it could be improved all that much. I was wrong, v13 is just plain slick. Congrats to those involved in it's design.
Didn't think I'd be thrilled with facegens with transparent backgrounds as I liked my many ballpark backgrounds. I may miss those "ballpark pics" a bit but the larger facegens really do look great and I'm glad they are there. I guess size does matter.
Skins:
Classic is very nice though I preferred it with the green background in the stats area Markus showed in the first screenshot. Hopefully it will be brought back in a patch, but even if not this will be my preferred skin.
The blue is a bit bright for continuous use for my eyes though I also think it looks great. I may use it from time to time.
Dark skin reminds me of the old "black light billboards" the bowling alley used to have in the '70s. Kind of a weird glow about it. It looks cool but not sure it is something I will use. Who knows, it may grow on me.
My only complaint, as Cras and MizzouRah already mentioned, is the removal of league leaders on the standings page. I play one game at a time, check newspaper and standings, and then move onto my next game. I play with the Cubs and checking the standings page is where I am able to keep an eye on how things are progressing not only in my league but especially the American League. Without leaders on standings page I will either miss out on the information or have to take the time to go to other screens to keep up. Adding steps to get information, that was easily accessible in earlier versions, due to removal of a working feature is a step backwards. It's not a gamebreaker but it is a situation that makes me shake my head
I am very disappointed with this decision and hope it can be "fixed" in a patch.
Overall though v13 is a huge step forward. Markus, Andreas, and all of OOTP developments should be proud of their accomplishment. Their work ethic and dedication to the game is what brings me back year after year.