I am not talking about someone with superpowers in a colorful costume. That can, and does, cover plenty of Occupations in this game and therefore does not make one a superhero. (Or a supervillain for that matter.) I am talking about taking a campaign that would be normative for something like Champions or Mutants & Masterminds (or, of course, Heroes Unlimited) and using it in the environment of RIFTS. This is all about the tropes and not the numbers or the gameplay options.
A superhero game in RIFTS can handle the same range of power level--from the streets and backwoods of mostly-mundane characters to the cosmic levels of Lensmen and their inspirations (Green Lantern and Nova Corps)--so that is not the issue. The issue is that such a campaign will not be the Comics Code Authority sort of castrated content; this doesn't automatically make it an Iron Age (to use comic culture terminology) setting, but it does mean that you are not making the most of what's available in RIFTS if you sanitize things.
By necessity, you should be using some form of team as your campaign template. The trick is to pick the right team for your table's needs; if you have a group that can reliably fulfill a regular commitment to show up and play for four to six hours a week playing the same characters, then you want to use a group like The Fantastic Four or one of the many Japanese tokukatsu shows (or their animated counterparts, Magical Girls and Martial Boys). For a group with a rotating attendance, you want to use a larger organization where members come and go routinely for this or that reason, such as the Legion of Superheroes or the various Avengers lineups. This also means choosing team templates means choosing gameplay templates; committed single-character groups can better exploit serial drama tropes and premises than looser groups who either lack commitment or play multiple characters, who (in turn) can better exploit episode structures and tropes.
So, that said, here's a list of things you need to do to make it work in RIFTS:
- Choose a Scope & Scale: On Earth, you're best being a City Defender sort of team, even if it's not strictly a city-centric team. Tolkeen is very good for a Magical Girl/Martial Boy team, using magical armors and powers with a common theme. The Coalition would do a super-elite team in the fashion of Suicide Squad or Doom Patrol, using some varieties of Juicer and Crazy that are otherwise ridiculously powerful but burns them out really fast- faster than what is the norm for Juicers. Smaller cities would work better for smaller groups, or even motivated solo players, but should also range somewhat afield to make up for the small city space.
Out in the Three Galaxies, go cosmic. Characters should have technology or magic equal to that of starships, if not star fleets. They should be concerned about large-scale threats; planet-specific parties should be irrelevant nuisances if they are not on planets of strategic importance, and those that are not irrelevant should make the power but lack the scope of operation for some reason or another in order to prevent "Why are they not major players themselves?"
- Cull Your Corpus: You, the GM, needs to sit down beforehand and sift through everything that is available and cut away everything that does not fit the specific superhero experience that you want. This means both what players can access as well as what the NPCs--friendly, neutral, and hostile alike--can access. By definition, a superhero is an individual whose capacities exceed the norm for his environment; if the standard soldiers or gendarmes are augmented in some fashion then being similarly augmented generally doesn't cut it- the superhero possesses an advantage of quality over the far superior quantity of the NPCs. This means that power differential is both relative and necessary to quality as "super"; Batman is super over most of what he deals with, but ordinary versus what Superman can and does contend with (which is why Batman has to rely on Writer Bias to prevail), so don't think that you can blindly employ what's in the books.
- : Get the players on the same page. You're playing a campaign that doesn't necessarily jive with RIFTS as-presented. Ensure that your players see things your way and agree with that before you start chucking dice. If this means house rules, do it. Square that away now, before any issues arise.