Though it is, and consciously so. But in an interesting way. As is often brought up in discussions about Portal, the aspect of it we ultimately spent all those hours jaffing off excitably about was its characterisation, its narrative, its voice-work - but rarely its portals. It's telling that Epsilon's one-man creator EON started work on the game before Portal was released, but following its announcement - i.e. during that period when we did all expect the puzzles to be the game's finest element. It starts with the same basic space-rift navigation concept, but then ploughs much, much further.
Even the setting's a whole lot more serious about this science business than Valve's mini adventure:
"In 2008, the largest particle accelerator ever created, the LHC at CERN's particle physics lab in Switzerland, was activated for the first time. The research obtained from this experiment has revolutionized the way we think about science. Un-answered questions that have puzzled man since the dawn of humanity are finally being answered. Are there extra dimensions? What is dark matter? Is time travel possible? Epsilon Experimental Sciences Research Facility aims to discover the potential of this whole new world of science, and you have been appointed as the primary test participant."
So, my presumptive sneer turned within minutes into the furrowed brow of intense concentration, as I plunged into increasingly complex challenges of my spatial awareness. Alongside - as in simultaneous to, not alternately - the portalling is time-freezing, time-reversal, gravitational inversion, black holes and, well, generally enough concentrated maths in action to make me need a lie a down after each level. It's sometimes brutal, in an entirely positive sense.
The question has oft been asked: what more can a Portal 2 do with the concept? Going on this, the answer is obvious - give the Portal gun a few more time and space tricks.
(Thanks to Mike C for the tip-off.)