I would say pretty hard as a series but Prime 3 is definitely the easiest, i rarely saw the death screen until i started playing it on hypermode. Even though the controls are different, having played the other two makes you more tuned in to boss tactics.
Be sure you experiment with weapon combos on the smaller enemies too. Combinations of rapid fire, charge beam, missiles/ice missiles etc. Some enemies you could spend a minute or more trying to kill on hypermode if you just blast away but with the right weapon selection you can knock them over in 10-15 seconds.







