I've been playing Raid for a few months now, and I'm finding some of the game mechanics very tiring.  I'll start with the least irksome and work my way up:

Tag Team Arena:  Waste of time even trying.  I have one rank 6/60 character and run through the lists on a regular basis looking for anything that I have even a small chance of defeating.  Only players that are willing to put in low level defensive teams have given me any chance of winning.

Summoning Shard Roulette:  I refuse to spend real money on any of the shard packs, because I know I'm going to get the lowest possible characters.  If there is a re-balancing system that improves you chances of getting a Legendary character, I've yet to see it in action.  All of my higher characters have arrived as reward.

Artifact Upgrade Roulette:  Honestly... WTF?  The level of frustration trying to upgrade artifacts is excessive.  You will note that I am trying to be polite here, but I could be exceptionally rude about this issue.  Pouring hard earned silver into a bottomless pit is so annoying.

And finally..

Character/Team Power: Taking a team into the arena with 51k power and watching it get ripped apart by a single character with 11k power, whilst unable to return any visable damage, is... (polite mode engaged) more than a little frustrating.  Why have a power rating when it means absolutely NOTHING?

I have invested an amount of real money into Raid, however, I am more than reluctant to continue to do so.  This is gambling of the worst kind.  Real money only provides the opportunity to receive the absolute minimum and, as such, is not worth the investment.

Raid has lost me as a paying customer, both on this, and the other related games I was thinking about playing.