At a cost of 5 to play, to get your best from this you will want to play ice of 7 or greater IMO. With 5 influence, probably won't be used out of faction.

www.netrunnerdb.com

In faction Hadrian's Wall, and Curtain Wall are a beast to Rez, but for 5? Not terrible.

Even Orion, which can become cheaper will still cost 3+6=9 or 4+3=7 if you put counters on it manually.

I guess it's a poor corporation's Modded?

Similar to the reviews of Tennin Institute: The Secrets Within and Saraswati Mnemonics: Endless Exploration, you can advance a card, even if it doesn't specifically say you can. This adds to the mental games of netrunner,

Did the runner run through the remote, only to find a token on the PAD Campaign?

Are you tricking the runner to hitting the remote, where you have stored an ambush? Or are you slow playing a 3/1?

When you put this and another card down, was it perhaps a 4/2 or even Vulnerability Audit? Rez this, advance for free and AAA to score next turn?

Gatekeeper is strongest when it was rezzed this turn, so it would combo with cards that allow you to derez your own. Cards that help you get more activations from the rez strength ability are needed to help combo.

Blue Sun: Powering the Future to replace this where needed, with another strength boost. (Thanks blackcherries)

The Foundry: Refining the Process can fire and get you more of these, with the help of other cards below.

Divert Power makes something cheaper while you get to trigger this rez strength again.

Test Ground allows you to fire the trash ability, derez Gatekeeper, and then re-rez Gatekeeper with unexpected strength.

Other combos, provided you were using them already

Isabel McGuire

Replanting

Plus, Gatekeeper is cheap and might give you some recursion of used cards if you can catch the runner flat.

Is it for every deck? No. But it might have a place in some.

(Edited to remove bioroid research reference and added blue sun)