(Revised original concept based on feedback)
So, a race of humanoid aliens have invaded and are planning to wipe us out for some reason or another (apparently we offended them somehow), and after a brutal and sudden opening, both humanity and the aliens eventually find themselves locked in a stalemate.
Despite the aliens having some form of interstellar technology, both sides have more or less fought to a draw, since their weapons technology doesn't appear to be much more advanced than our own. However, we have much shorter supply lines, so we can afford to expend a few more drones and missiles than them.
While the worlds various Navy's and Air Forces struggle to keep shipping and flight lanes open and prevent the invaders from taking control of the skies, the ground forces are stuck trying to dislodge what ground forces the aliens managed to land. This is proving difficult as the aliens have settled in for a siege, and their ground-based defence technology is several steps above our own. Primarily, their bases are defended with some sort of select frequency EMP shield and various anti-air and -rocket/missile system that renders them virtually immune to any air-based attack short of a sustained saturation attack to overload their defences.
While the various land forces figure out an optimal strategy to destroy the alien land bases, the aliens themselves begin a campaign of terror strikes targeting various civilian population centers and industry. This is rather effective until they target a laboratory belonging to a rather unremarkable and privately funded genetic research company, the reason being a few leaked pieces of security footage showing several members of the sites security personnel defeating the would be aliens in CQB seemingly unaided.
This causes a bit of a stir worldwide, as the aliens have been noted to have increased levels of physical performance compared to humans, with various critics citing the footage as fake and a propaganda stunt - until the company confirms that it did actually happen.
They go onto explain that they were profiling the aliens genetic material for weakness to various chemical and biological agents, when a researcher discovered several genes that controlled motor unit co-ordination in muscles and tissue recovery for various organs, allowing for more effective healing, essentially borderline organ/soft tissue regeneration. Furthermore, in a nearly impossible genetic fluke, the genes are somehow compatible-more or less, with the human genome, and with a modified retrovirus as a delivery vector, an intensive month-long gene therapy procedure was developed.
Despite various protests, lawsuits and complaints about 'playing God', they defend their research, presenting evidence that modern-day genetic science could have discovered something effectively similar within several decades - or a lucky genetic mutation.
I'm primarily interested in the plausibility of the various aspects of my scenario - Is the fact that the aliens, despite being from a much more advanced society, have weapons technology that isn't much more advanced than ours? Would alien forces trapped on the ground resort to terror strikes against civilians to force the governments to reassign military assets to protect them? The fact that a select few parts of their genetic material are essentially somehow compatible with humans, the biological effects of the improvements are plausible, and the duration of the enhancement procedure and the non-alien-influenced development time for said enhancements. I know that the ethical concerns around genetic engineering are real enough - I need only look at the news.