Red Cards

I guess a challenge from behind, away from the ball is only worth a yellow. Yeah, that makes sense.

Referee gives too little red cards, i agree.

Don't think I've even seen a red card given after a penalty fault.

This is a definite flaw.

The above, about penalties, i agree with. You very rarely see a penalty given and a red card follow.

Also, denying a clear goal scoring opportunity/last man situation's don't usually equate to red cards when they should.

I find Refs give red cards for stupid things and yellows for actual malicious tackles. My main problem is when people get elbowed, IRL many refs have different views on how to treat an accidental elbow, but most of the time players see a straight red after accidentally elbowing another player. On the other hand, reds are never given. Marcelo, my left back, often bends the rules due to his competitive personality. He gives away many fouls just outside the penalty area. He got yellow for trips from behind as last man, but has never seen red...it's odd

Agreed. There's too much randomness involved in yellow cards, often in one match players will get yellow carded for an upending in the middle of the pitch and then not get yellow carded for holding a shirt in a dangerous area. And red cards for blatant fouls are missing for the most part.