It often takes awhile with a codex to find that hidden gem that makes your smile. A gem is a combination, or special wargear or character that just pulls everything together. For example.....
These were not my first impressions of the codex, but were the hidden gems, combos, that I discovered later on, that were highly effective.
Im not through re-reading and re-reading the Blood Angels yet, but a little gem I discovered recently was The Sanguinor. My first thoughts were wow, too expensive to even consider. Mephiston was a better powerhouse on the field. However, the Sanguinor, basically turns one of your seargants into a character. Gives him +1 Init, WS, Att, and Wound. When the Sanguinor is deployed, is when he chooses (random) which seargant, meaning you would have to build a list with this in mind. I'm not a fan of random selections (thanks GW), but imagine this..... An assault terminator sergeant with an extra wound +1 init, etc... 275 pts, gets you basically two characters, and if the Sanguinor is within 6" gives that unit an extra attack. Basically our terminator with lightning claws would get 6 attacks on the charge. With a chaplain, he hits on a 3+, re-rolls misses, re-rolls failed wounds, which can wound on a 3+ if a priest is near or has the red thirst, all at init 6. You could get all this.... and wait... you also get The Sanguinor.
Finding the gems that you like within each codex takes a little patience and re-reading. I think though that each codex has its opportunities and its just a matter of you reading them to figure out what it is that you like about the army.