Strengths:
1) Top army in
40k for quality shooting (not quantity though, that's orks or guard)
2) Hammerhead is arguably one of the best tanks in the game
3) Railgun is the best anti-tank weapon in the game
4) Able to be extremely mobile and probably outmanouver any army except Eldar/Dark Eldar
5) Crisis suits can be tailored to face any specific threat (tanks, hordes,
meqs etc.) or just be used as a general all-comers unit
6) Markerlights
7) Majority of your units able to gain BS4 or better.
Weaknesses:
1) No real ability to seriously counter assault units
2) No real assault capabilities
3) True Line of Sight forces you to be more careful with Crisis suits now
4) Tends to be an expensive army point for point
5) Easy to learn, difficult to master.
Don't play Eldar, but hope that helped
3)