Long time Football Manager player, since CM98 I've bought every single one without fail but with FM15 I feel this maybe the first one I miss out. This is not because of the ME which is better than FM14s nor the actual mechanics of the game but the general interface which is in my opinion a step backwards in many areas.
1. General UI:
Dark skin is default is difficult to read since their is not enough contrast between the background and the text. If Opacity is the aim the menu backgrounds have to be a lot less opaque.
Font is difficult to read and not too easy on the eye, my biggest complaint is it's too thin and too 'fun' for FM which is characterised by a professional approach
2. The Sidebar
Whilst neat takes up large part of the screen (esp on a 13 inch 1280x800 laptop) feels like the screen has been cut by a third, is not expandable or retractable into icons without headers adjacent. The changing sidebar colour gives the UI an amateurish feel and unlike FM14 where you could pin locations to the toolbar everything is fixed in the sidebar.
3. Player profile:
Default colours are barely distinguishable light green is barely different to the darker shade so good and great attributes just blend in. I know you can change this but it's a strange choice and makes a bad first impression. In FM14 dark blue stands out from lighter shades which emphasises the good part of the player's game.
The awkward position of ‘Vision’ Attribute. I can understand why Vision replaced the generic all encompassing "creativity" but the placement of Vision splits up teamwork - work rate and displaces it from decisions. I think SI should think about listing attributes by how closely related each attribute is to each other, e.g First Touch, then Technique ;Crossing then Passing and not alphabetically (or at least have the option in the preferences to list in either form.)
The hyphen that lists neutral in attribute changes is large and obnoxious unlike fm14 which is much more discreet.
Important actions like 'Offer New contract', 'Make an Offer' and 'Get Scout Report' are hidden in sub menus. I think this is a bad move since they're important enough to stand alone and so requires the user to dig into the menus to find them instead of being immediately apparent. I understand SI wanted to reduce the amount of toolbars until the core content is displayed but perhaps being able to pin certain actions independent of menus would be best.
4. Tactics screen
As has been mentioned before the tactics screen is a step backwards from FM14.
The pitch player icons are in my opinion a bit too large. Player's don't take up that much of the pitch even though it's illustrative. The pitch no longer at first glance shows player roles, this has to be accessed from the left side of the screen and so forces the player to constantly switch from left to right.
Strange choice of colours to demarcate player positions for e.g purple for DMs?? Black for strikers?? The icon that supposed to resemble how competent a player is in a position being represented by the length of an oval is a step backwards from the star rating system in FM14 or the traffic light buttons of FM12.
'Show Realistic targets' are hidden under a filter sub menu and is not immediately visible, this is a shame as it's a much needed attribute which now take 3 clicks to show.
Icons in a player scout report loosely resemble the attribute they are supposed to represent. For example a link in a chain represents intelligence?? Surely a brain or a light bulb would be better?
Black star to denote unsure is bad colour choice, opaque, grey or a lighter shade of gold would be better. Even better would be a flashing star but this may be too complex to code.
Other than that I like the new changes, the new tactical options such as distribute to full backs, the positioning of player's on a pitch depending on mentality/role etc but the crux of the issue of a game like FM is usability and I think it's a step backwards in this area.