To be honest, I was dead set againt a series going back in time. A prequel. Star Trek has been about looking forward, not back.
But I thought I'd give it a chance. And it turned out that I did like it after all, for the four seasons it was on.
We first meet Captain Jonathan Archer as a young boy, asking his father when his ship (a warp 5 ship) will be ready. It's not for a long time. The father will die, and Jonathan Archer will be the first captain of a warp 5 Starfleet vessel.
His Chief Engineer is a long-time friend, Commander Charles Tucker III. His friends call him Trip. He's a laid back guy with a Southern twang but also a genius when it comes to engineering.
Subcommander T'Pol, later to be Commander T'Pol, is the Vulcan Science Officer. Dr. Phlox is a Denobulan assigned to Earth thanks to an Inter-species Medical Exchange Program. He accepts an offer to be Medical Officer on Enterprise, a post he's offered since no human doctor had ever even seen a Klingon, which is pertinent to their first mission. They are the only 2 non-human crew members.
Lieutenant Malcolm Reed is the Armoury Officer, a by-the-book British Starfleet officer with a penchant for blowing things up, responsibly, and hopefully symetrically. We'll find he has a rather good grasp of engineering as well as he pulls off some near-inventions of his own.
Ensign Travis Mayweather is the helmsman, a boomer who has spent his whole life in space with his family on a freighter called The Horizon. Ensign Hoshi Sato is a linguistic genius. She hears a language and can soon parce out it's meaning. She's the Communications Officer, naturally.
So, as far as I'm aware, the Enterprise is a first, Starfleet's first true starship, just set out on its maiden voyage, and too early at that. Seems this Klingon needed to be taken back home, so the launch was moved up. The Vulcans, the only aliens we humans really know at this point, are skeptical and assign a Vulcan sub-commander to the crew as a science officer and observer on this mission, in exchange for providing star charts.
While humans and Vulcans get along, they are not the best of friends. The Vulcans are skeptical of humans' abilities, sensibilities, responsibilities, etc. The humans feel like the Vulcans are hiding something, a lot of somethings, and looking down on humans in a parental way.
When the Klingon gets captured by the Suliban, T'Pol, the token Vulcan, proclaims the mission finished. But Captain Archer and his human crew are not so easy to give up. A rescue mission ensues, taking the crew to Rigel and, later, a conglomeration of Suliban ships all stuck together. They do rescue him, but they also learn of a "temperal cold war" in doing so, and Archer finds himself in a fight with a futuristically-enhanced Suliban. Only the new transporter, which hasn't transported humans up to that point, saves Archer from death. The mission is accomplished and the Klingon is returned home. Humans have succeeded where the Vulcans didn't think they could.
Archer asks T'Pol to stay on board, and she agrees. She is second-in-command, with Tucker, the Chief Engineer known as "Trip" coming in third. Lt. Reed, a by-the-book military man, is the Tactical Office. Ensign Mayweather, born and raised on a freighter in space, handles the helm, while linguistic genius, Ensign Hoshi Sato takes on the task of communcating with aliens we've never met before.
In time, we see Enterprise and her crew meeting new aliens, and interfering with primitive cultures as if there were no Prime Directive. Wait. There isn't a Prime Directive. Yet.
We find the Vulcans have been spying on the Andorians, and lying about it. A legendary Earth colony that disappeared years before was detroyed by a meteor, leaving only children to adapt and build a new civilization on Terra Nova. And the Enterprise gets a taste of future technology when the Suliban come for a visit again.
So far, we've met the Suliban, the Axanar, the Nausicans, the Terra Novans (humans, but not of Earth), the Andorians, the Coridan, and a variety of others on Rigel.
More species: Valakians and the Menk, Tessnians, Tandarians.
Well, that's it for now. Let me provide you with some links to learn more.
TrekGalaxy's Enterprise pages. Lots of info and Interviews, etc.
EnterpriseLog.com, a page with lots of information and fun stuff.
All Things Enterprise, Just what the title says!