How you judge this “Iron Man” threequel depends upon what you expect from the franchise. If good performances, comedy and scientific silliness make your day — you’re in. If you’d hoped for brilliant action, blow-your-hair-back romance, or some excitement — you’re out. Since I’d wanted some of each, I guess I’m half in.

The film’s best action sequence occurs in Tony Stark/Iron Man’s basement, during an early scene that finds the inventor obsessively tinkering with a stable of prototype Iron Man suits. Perfecting the arrogant, snarky, yet vulnerable genius whose challenges surely mirror his own, Robert Downey Jr. continues to elevate these films. Stark ignores warnings from his computerized advisor Jarvis (voice of Paul Bettany), reminding him that Stark’s new technology is untested and dangerous, as he commands an Iron Man suit to fly to Tony, one piece at a time — automatically latching onto his body. The comic suspense caused by clanging, misfiring Iron Man suit pieces, reaches its apex when the suit’s cod piece and face plate make beelines for their targets.

Tony has also programmed his suit to walk, talk and fly while he controls it from a remote location. In a misguided effort to kill two birds with one stone, Tony sends his Iron Man suit to consort with live-in girlfriend Pepper on date night — allowing Tony to continue tinkering in his basement.

In addition to functioning as Tony’s conscience and etiquette advisor, Gwyneth Paltrow is finally allowed to showcase the charms that persuade Stark’s dependence upon and complete trust in her.

Stark’s reckless behavior causes other problems to appear on Tony’s horizon. A flashback to 1999 reveals that he once played a cruel practical joke on handicapped, wealthy scientist Aldrich Killian (a flashy Guy Pearce). Payback comes 13 years later — though this somewhat incoherent plot never explains what prompts Killian to use a scientific breakthrough for evil rather than for good.

Ben Kingsley is typically wonderful as a Bin Laden-like terrorist, beautifully handling the surprise twist associated with his character. That twist, a well-written and well-executed comic time-out, is a it’s a wonderful cheat although it deprives us of an emotionally satisfying payoff.

Don Cheadle, reprising his role as “War Machine” — renamed “Iron Patriot” — remains Stark’s only friend and ally, but here he is merely filler.

In order to further flesh out Stark’s character, the scientist escapes to nowhere, Tennessee, where he temporarily teams up with 9-year-old local inventor Harley.

Could it be that the producers have found the next generation to succeed 48-year-old Downey? Why not? Sporting the fussiest hairdo since Justin Bieber’s debut mop, Ty Simpkins steals scenes from Downey using a combination of Simpkins’ sweet-faced charm, comic chops and sly smarts. Having no children of his own, Stark sees himself in the lonely little boy who deals with his daddy issues by creating cool machines. Son of Iron Man. It has a nice ring.