I think that the Vindicare and primaris have shown up a lot of the upper-level limitations of the DH rule-set.
In using a percentile system it is very difficult to create playable normal humans and still fit space marines and lords of change on the same scale while retaining the drama and tension of success/failure in combat at the table.
A few tweaks that I use -
1. 96-100 is an automatic failure in all rolls.
2. Unnatural attributes give you a +3 to your stat bonus per multiplier you attain.
3. Vindicares get an extra reaction per round which can dodge the undodgeable. Their gimp suit soes not give them +10% to dodge.
4. The effects of most psyker powers are based off psy rating rather than Willpower bonus as per Rogue Trader. Still working on a lot of conversions for this.
5. An idea that I was considering was a passive defensive score. This would be a penalty to attacks on the character (that he is aware of) based on WS bonus for parries or Ag bonus for dodges. I may also put in a way to make your attacks more difficult to dodge/parry as per the fast quality. Still trying to figure out where to set the ratings but that may be a good way to put the edge back into duels between Uber-PCs and BBEGs. When an ascension PC with WS 70, a best quality power sword and blademaster attacks he almost always hits. Likewise his foe with similar numbers almost always parries. If each had a -20 or so to both rolls then suddenly the battle is interesting again. If we tie the defense score to high-end talents then PCs can still pwn mooks but need to use trickery and tactics in the end of level boss-fights.
I must say that I am worried about Deathwatch and I do not envy the chap with the job of trying to shoehorn marines into the BRP skeleton of DH. That said the design diaries seem to be focusing on more indy concepts to build the kill-team so it looks interesting and i will definitely buy it.