The game can be hard if you just pick your team, choose your tactic and let the game run.
Personally, I dont have a problem with it. After a season of two of getting my team (Spurs) together I am able to challenge for honours nearly every season.
During a game I am often changing tactics to counter those of the opposition. There is no point selecting a attacking tactic and sticking with it, and you wonder why in the last 5 minutes you conceed lots of goals. Your players will tire due to the excessive demand of constantly attacking that they leave gaps for the other team to exploit. Quite realistic to me. Also, there is no point just setting any old tactic if the players you have cannot fulfil the requirements you have set. No point using attacking wingers if the players you put there cannot run, or cannot cross a ball.
Also, you need to latest patch to fully appreciate the game. The original out of the box version has AI bugs that make games seem one sided, and lots of red cards and injuries. So, download the patch and then restart the game, you will notice the difference.
Remember, its a management sim, simply expecting to win by buying the best players, and setting a tactic up and not changing it wont bring success.