Of the ones I've used.... tone and notes on fan player culture
GURPS: the tone is almost always somewhat gritty. There are issues with the fanbase's culture; GURPS fans have a tendency to warp settings to fit GURPS, rather than the other way round, and tend to be GURPS über alles in mentality. SJG has definitiely warped settings to fit GURPS, most notably, GURPS Ogre, GURPS Vampire, GURPS Mage, and GURPS Autoduel 2E. Players tend to favor attribute for point saving reasons, as raising a point of IQ or Dex often costs less than raising the 5-15 skills that will get a +1 would.
Palladium: the tone is always somewhat heroic, and the rules flat out explicitly do not have social skills. The player culture often is about who does the most damage, and/or who pulled the biggest social score, as that latter is always PvGM. The world building is really good. The system plays well enough, but combat is a lot of opposed rolls, and until recent printings, not always easily understood as to flow. Player culture tends towards the younger and poorer side, as the books are relatively inexpensive, durable, and often flow through used bookstores. All characters can be crossed to just about all other settings without issue.
CORPS: The tone is flatten your molars level gritty. Fights hurt. High skill matters. Given the constraints of the character gen, competent PCs are scarily effective in their fields. Optimized characters can do called shots without rolls once per second... I stop short of saying it's "realistic" - as it allows the .25ACP to be a real threat of a firearm. Note that attributes and skills are from different pools, so characters are literally forced to spend points in certain areas. Fan Culture tends towards tinkerers. Published settings are skill-heavy, and somewhat grim.
EABA: Tone is much like D6 system; can do light to heavy, but skill matters, and attributes provide a minimal competence in everything. I can't judge the player culture much, since it's so little known. I'll note that during the playtest, I used it for the Traveller OTU; I was able to do everything I needed with the core rules. The TN's are directly comparable to those in Traveller or 2300. Mechanics are attributes generate dice codes in the 0d+1 to 4d range; skills add 0 to 5 d, all dice d6's, roll the pool and keep best 3. Ironically, most of the official setting books are extremely grim.
BRP: tone is heroic, generally, but certain settings tweaks can make it grim heroic or even grim victims-on-adventure. Damage hurts; combat is unrealistically permanently disabling in some editions. Fan culture is more varied than the rest, IMO. Generally, BRP fans seem to play multiple settings using it, often bespoke standalone cores with minor adaptations. Best noted for Call of Cthulhu and RuneQuest, which have very different tones, but very similar rules.
Hero: lots of math in CGen; tone from mundane to super epic, by options and campaign limits, defaulting to lower end of 4-color supers; 75pt Fantasy Hero is definitely heroic in tone. Player culture is varied, but universally math tolerant. Rules are very flexible, with lots of options. Corporate culture twists game rules via setting rules to fit genre. I've yet to see a character concept than cannot be accurately portrayed using HSR 4/5/6, but many are well outside the realms of normal point totals. (Greek Gods in the low thousands of base points, for example. And that's official!) I'd not recommend it for film noir, tho' an adapted core did just that...