Fifa 21 has been a huge improvement from most recent years. The most noted improvements are in career mode. The training schedule has a more in-depth program, that you can individually set for each player, for which attributes that you wish to specifically focus on & improve.
The most greatest career mode improvement this year, in my opinion, is that you can train players to play in new positions - I love this! as you can train a player to learn and be versatile in 3 or 4 different positions, or many as you wish.
As for the gameplay itself, I feel that the co-ordination of player movements and reading of the game is more advanced I.e players will read through ball passes and make timely runs better (although off-side awareness) can be very poor at times and annoying (you will however notice this happen more with youth players or lower league players).
Another slight improvement, Is the youth development system. It is still long winded and time consuming to filter out the best youth players, but I have noticed with paying close attention to detail, the overall quality of players is slightly better.
I feel the most noticeable Improvement in this year's fifa installment, is the career mode-match simulation options. You can see that they had put some real thought into improving this. I really like that you can watch the match in a tactical overhead view and that you can intervene, in and out of gameplay, to change the influence of the game!
Player Attribute Ratings:
The reason that I have lowered my review from (5) stars to (4) is purely because of the fifa player ratings, especially the contrast of stamina ratings from last year to this year, as this plays a huge factor of the recovery in between matches, which can be a complete nightmare, as when you're playing in a month of congested match fixtures, due to league matches, cup ties etc. Also, some of the english premier league player ratings are appaling - Look at Newcastle United's (Andy Carroll) for example, how can EA justify a stamina rating of "32" for the sheer ability and calibre of this type of player. As it stands, according to this rating, he would hardly last 30min before getting very fatigued with the fast pace of my tactics.
Transfer Market: (Career Mode)
Some minor improvements in the player transfer negotiations, loan buy options etc. However, the (non-extentsion) option in negotiating the length of contract, seems completely pointless???
Negotiations are very intense and I like that it has been made harder to secure free transfers via the last 6 months of players contracts. In contrast to last year, players will sign new deals with their current clubs (right up to the open window) so I would strongly advise that you employ a strong scouting network in advance at the start of each season, according to the club that you are managing, with the financial resources that you have. This will play a big factor, especially for lower league clubs - I'm currently managing english league (2) Barrow AFC, so I can speak from experience on this (great club still).
Addition of the vanarama national league and EFL stadium's would be most welcome and appreciated next year ;)
Update: 19/09/2021,
Very annoyed! at multiple sources claiming that the Vanarama National League was going to be added to the Fifa 22 edition. I'm even more annoyed with EA sports for now confirming that they are not going to be added. Their is a clear demand for this league to be added to the game and consumer feedback is clearly not being taken onboard. Very disappointed with this EA Sports!