"On The Shoulders of Giants" is the name of the achievement that pops up towards the end of XCOM: Enemy Unknown, Firaxis' reimagining of the revered strategy classic X-Com: UFO Defense. The achievement is awarded when you pass the final bottleneck into the game's finale - put another way, nobody who finishes the game could possibly miss it. Firaxis want to make the esteem in which they hold the 1994 original unmistakably clear.

You can't blame them. Microprose's idiosyncratic sci-fi strategy game had captured hearts all over the world but also steeled them against imitators. No official or unofficial sequel to X-Com had ever met with widespread fan approval. Otherwise perfectly competent games like the UFO Extraterrestrials series and UFO Aftershock and its sequels were dismissed as "not X-Com enough."

What was that elusive magic that the original had and no remake had successfully recaptured? Jake Solomon, the producer of Firaxis' XCOM wasn't even sure that he knew.

"I'm a very hardcore X-Com player," Solomon told me, "and if you'd gotten ten of us in a room and asked us what that 'Xcom-ness' is, you'd walk out with ten - no, probably twenty answers. And I didn't know that I had nailed it." Original X-Com designer Julian Gollop has long been held up as a man who caught lightning in a bottle, and X-Com itself a unique feat that would never be repeated.

The XCOM remake manages to be both faithful and radical in its interpretation.

2K was always careful to show the original game its due reverence in their marketing. Solomon himself was a staple of the pre-launch hype machine, where he repeatedly and convincingly put his True X-Com Fan bona fides on display in countless interviews. When asked about Gollop, Solomon told PC Gamer in February, "[h]e's a personal hero of mine so I've tried as much as possible to honour him".

Talking to Solomon last week - the day before American Thanksgiving - I had caught 2K's producer at his most relaxed. With XCOM's release in his wake, Solomon is getting used to the slower pace in life. "It's weird when you're a developer, because oddly everything ends when the game comes out. You work like crazy, the game launches and then everything just stops. I'm mostly just sitting on my ass." I tell him that I had talked to Julian Gollop about XCOM - his XCOM - and I felt Solomon's post-crunch holiday cool fumble for a second.

Solomon groans loudly. "Oh great," he says. "That's like hey, 'I heard you're making a movie of For Whom the Bell Tolls - I just talked to Hemingway about it.'"

Solomon's distress is rooted in the fact that part of him feels like he got away with something when XCOM came in for all the praise it did. "There's no way to understate this: we redesigned the game." Solomon's voice drops a little when he says this, like a man confessing to profane acts in a temple. "We threw out time units, we threw out inventory management. We redesigned the geoscape from the bottom up."

Aside from a few fundamentalist diehards for whom no remake will outshine the nostalgia-glossed perfection of the original, X-Com fans have welcomed the new game, a fact borne out by solid sales numbers and respectably high review scores all around. But if the new XCOM has received a warm embrace from fans and critics, what has original X-Com designer Julian Gollop - Solomon's "personal hero" made of it?

You can relax, Jake Solomon.

"I think Firaxis has done a great job," Julian Gollop told me. The legendary designer of X-Com and Laser Squad has recently settled jumped ship from Ubisoft to work solo on remaking his 1985 design Chaos from his bedroom in Bulgaria, but the new XCOM has taken a good chunk of his time. "The game is addictive and absorbing, not to mention quite challenging on the classic difficulty setting." Given that the original X-Com was infamously unsentimental about mowing down the player's squaddies by the Skyranger-full, that's some remarkable praise.

Prior to the release of the new game, many X-Com fans howled at the decision to develop XCOM for both PC and console, unlike the original and Firaxis's flagpole franchise Civilization. And while this new XCOM is decidedly more streamlined than the 90s-era source material, Gollop sees nothing wrong with the nips and tucks. "Most of their decisions have been pretty sensible, and they have made a very console-friendly game. Overall I think they have preserved the essence of the original X-Com."

Not all of the streamlining meets with Gollop's approval, however. "One small disappointment is that the positions of events and bases in the world view have no relevance at all," Gollop said, comparing the new game's single-base approach to the original's player-driven expansion of bases around the world. "I often get the feeling that some things are just too deliberately contrived. The three simultaneous abduction sites [of which the player can only respond to one] being the worst offender.

"Oh great. That's like hey, 'I heard you're making a movie of For Whom the Bell Tolls - I just talked to Hemingway about it.'" - Jake Solomon

And like the original, XCOM is as tough as boots.

"The original X-Com had significantly more pseudo-random elements. However, it is clear that they have been following Sid Meier's dictum that games are essentially about making interesting decisions. They have strived to make every decision have some kind of trade-off."

The lead-up to XCOM's release revealed worries from the fans about game's art direction, particularly the liberties that had been taken with the original's iconic aliens. RPS's Alec Meer, for example, fretted about "unsubtle" designs for the new "generi-monsters". Gollop, though, loves the extraterrestrial opponents. "The design of the aliens is great, with some very nice animations," he said.

Well, almost all of them. "I find the thin men too comical."

Now engaged in re-making Chaos, Gollop finds himself in Jake Solomon's shoes. "Re-imagining a respected game from the past means that you shouldn't alienate the games fans," Gollop tells me. "I have a similar problem with Chaos that Firaxis had with X-Com. I may succeed, I may not, but I will certainly attempt it. I think fans of the original Chaos will appreciate it."

When I tell Solomon what Gollop thought, he's audibly relieved, as if I've just told him he doesn't need dental surgery. "That's good, man. The guy's a legend. It's a weird situation. You know he's still out there, you know he's going to end up playing it - and you just admire the guy so much."

Both men are recent converts to Twitter, and they've begun talking to one another on the platform. Besides tweeting, Gollop has been keeping a developer diary of work on the new Chaos. "I can't wait to see how his new project turns out," Solomon tells me. It's one thing to stand on the shoulders of giants - how often do you get to watch them work?