Modes:
-Arcade
-Training
-Versus (player vs player, player vs cpu, cpu vs cpu)
-Trials (each trial is shown for you via replay and button presses)
-Tutorial mode where it actually teaches you how to play and do effective combos, all while making it fun and rewarding to do so
-Challenges (challenge tower, weapon master mode)
-Story mode (MK9, MKX, Injustice - a mode where you are forced to play with all of the characters, with professionally voiced and recorded dialog, show that you put effort into the story and not let it drag out or be lackluster)
-Extra minigames (extra battles like Soul Calibur 2, test your sight, test your might, test your strike, test your luck, grab the coins, board the platforms, break the targets, multi man smash, break car, break barrels, minigames where it tests your abilities/reactions from characters, etc)
-Plenty of unlockables (Mortal Kombat 9, Soul Calibur 2, and even Smash Bros got the single player down correctly)
Roster:
-At least 25-30 characters with different play-styles, with constant DLC adding new characters round the year, not just one character every few months like SFV.
Stages:
-Bare minimum of 20 stages to start. Ideally every character should have a unique stage but that is tough. DLC should improve on this quite a bit.
Multiplayer:
-Good netcode
-Accurate matchmaking
-Ranked matches
-Casual matches
-Private matches
-Leaderboards
-Online lobbies
-Spectator mode in lobbies
-Online training
-Ability to play mini-games online
Misc:
-Get into games as quickly as possible and start having fun (UMVC3 and USFIV for PS4 are quick to load into matches)
-Do not launch a fighting game like SFV but don’t get over-ambitious and release a game with so many modes that are broken or worst of all, not fun. Take your time and get it right!
-Good UI and menus go a long way
-Listen to your fanbase and FGC on what they want
-Cross-platform play
-Ability to temporarily unlock all characters and stages for tournament play
-Reward players for continuously coming back to the game
-Give a sense of progression for unlocking stuff in-game
-Stat tracking (like Smash does it)
-Guest characters
-Create DLC after game is complete, like Smash 4
-DLC should make players want it and not feel like it's a cash grab/order from the top executives
-No microtransactions