Madden 08 and 09 will probably go down in series history as the not-quite games that preceded the '10 iteration.
Gameplay (7/10):
Madden 08 plays like an arcade-y, distorted version of real football. Again, this can still be a lot of fun -- but it can also be really annoying. On the field, there are a few distinct problems that mar the realism of the game that must be mentioned.
First, defensive backs are way too good at picking off the ball. As are linebackers, for that matter. They will leap five feet in the air, make one-handed grabs, and can do so with their back turned to the QB when the ball is thrown. It's just illogical; if a DB intercepts a ball in real life, he at least needs to a) anticipate and guess the QB's throw, a risky move; b) jump the receiver's route, which Madden 08 actually depicts believably; or c) see the ball coming and react. Now, the last option is really broken - on a ton of deep balls, the DB will never look back to the quarterback until the ball has been in the air for a second or two, then abruptly turn around and make the pick instantly. Obviously, it's because the computer always knows where the ball is, and that's just ridiculous. There should be AI routines for each player indicating their "awareness" of the ball. And when your back is to the quarterback and you're looking downfield at the receiver you should be covering, obviously you have no idea where the ball is.
Secondly, there are a ton of exploits that can be manipulated. There's the famous "rocket catch," though I never practiced enough to get that one down. But there are also far simpler ones. For some reason, crossing routes off of play action work really well - incredibly well - in this game. The crossing route is pretty hard in actual football, and takes a long time to develop, so that's not right. Also, the famous fullback dive play...if you own Greg Jones, call the fullback dive for every rushing play and you're guaranteed 4-8 yards on a 1st and 10 run. It's absurd to rack up 100 yards with your fullback with ease on All-Madden, while on the other hand your halfback actually has a lot tougher time getting yards on that difficulty setting.
That being said, the Madden series has been around for a long time and there are advantages. The game is very polished, and the controls are tight and responsive. Additions from past years like the Hit Stick and the Highlight Stick give you control over devastating collisions and wicked spin and juke moves. Sometimes, these become physically improbable and again detract from the realism, but it's a lot of fun to execute them, either to slam a ball carrier into the ground or to make a linebacker look silly when he slips to the ground trying to tackle you.
Defense is actually better than offense in this game. User control is really engaging when you get the hang of it (which admittedly takes a fair amount of practice). Controlling a safety is a blast: reading and reacting to a play make every single snap in Madden an exciting moment, and it's really a thrill when you act properly and blow up a play in the backfield, or get a user pick and take it to the house. I haven't played as much as a linebacker or a defensive lineman, but I personally found it difficult to get pressure on the QB as a lineman.
Gameplay Modes (8/10):
Madden 08 has all the features you could want, including full-fledged franchise, Superstar, single-game and practice modes. Superstar mode has been one of the best additions to the series, and I enjoyed steering the career of explosive running back Bossman Jettz as he played for the Dallas Cowboys and then the New York Giants. However, it should be noted that there are few positions that are actually fun to play, and it's also a lot easier to be on the offensive side of the ball rather than the defensive, since the game penalizes you for every time an opponent gets a first down or rushes for even a medium gain.
Franchise mode is still the meat of the single-player experience. It's deeply flawed as well - trading has some glaring exploits, including the ability to cleverly arbitrage and stockpile draft picks until you can pick up 2-3 of the top 10 talents every year. Alas, prospects tend to develop along odd trajectories. Almost all early-round WRs start out low but end up very good, rated between 85 and 92. The same thing happens with QBs and CBs, so by Year 10 of your franchise the free-agent wire will be flooded with people at those positions who are very solid starters or even borderline star players. On the other hand, good linebackers and defensive lineman are almost impossible to find. Rarely could I coax a drafted defensive end's rating up past 85 (while first-round defensive tackles slowly progress until they are 88-90), and linebackers were even worse. For instance, in Year 12 of my franchise, after all current players had retired, the best linebackers and defensive ends in the league were rated 84 or 85. This is puzzling considering that there are a healthy number of players at those positions rated 85-95 among the real-life players.
Presentation (8/10):
Though clearly outdated now, this game did look pretty good when it first came out. The grass looks terrible in retrospect, compared to newer games like Madden 09 or NCAA Football 09, which rightly touted their grass graphics as a marked improvement over previous iterations. Player models are still laughably beefy in this game - even punters look like 'roiders from Gold's Gym, and the defensive lineman are truly a terrifying sight to behold. It's like your entire 53-man roster dropped straight out of Conan the Barbarian or the comic books.