The 3rd season in general was a dissapointment to me (with the exception of around 7 episodes that were amazing and even surpassed the previous seasons in awesomeness).
The 26 episode format definetly had a negative side effect on animation quality with more eps having to spend their budget on, result: even with DVD upgrades the graphics were below that of 2nd season and the battles weren't nearly as well animated as in previous seasons and some battles were just plain dull to watch. I loved the battles back in season 2 and 1 (Dragonball Z could learn something from those battles XD) so this was hard to swallow. I'm not even gonna start about the like 10 episodes that were training fillers.
Another bad thing was that they introduced WAY TOO MANY NEW CHARACTERS!!! Almost none of them could get enough development, only 2 of the Numbers, Teana/Subaru, Nanoha and Vivio got development and many of the characters were just left out. I would've liked to see Elio's past as the small bits they showed were a lot more interesting then the story of Su and Tea.
To end my complaints about characters i'll say that a lot of characters were deleted from StrikerS and made only some cameo appearances. Show content
Nanoha's friends and family don't appear in StrikerS, Amy retired (was replaced) and Shirley took her place....who I didn't like nearly as much as Amy, Arf and Yuuno only appeared a few times despite them being main characters in seasons 1 and 2.
Music I can be short about. The best music in StrikerS were often re used songs from MSLN/A's which is never a good thing but personal taste, I just like the music from MSLN/A's a lot better then StrikerS.
The last thing I didn't like is that in previous seasons there were lots of hints for possible couples but there was no canon (probably due to everyone being 10 years old, age stuff...) so with the older characters in StrikerS everyone looked forward to having some canon but we ended up getting even bigger hints and still no canon. I don't understand why SEVEN ARCS decided not to have any canon in season 3, it would have made the anime a lot better (and bigger saleprofits ^^).
Don't get me wrong, StrikerS certainly is a good anime but it doesn't come close to MSLN and certainly not MSLN A's.