Are there a lot of references to the plot of the first game? Are there things I'm already expected to know at the outset?
I hear that there is some stuff imported from old save games in the new sequel. Is there content I'll miss out on for not having an old save?
I played the first one through and loved it. I'm now playing Witcher 2 and loving it as well.
If your concern is the plot and back-story, I think you'll do fine just reading the plot summary on Wiki
As far as importing a save game, it carries over a little bit of money and gear, but nothing that gives a huge advantage. You'll have earned more money and better gear in a few hours anyway.
The biggest issue I can think of is in understanding the mindset of the character, the game, and the world. The Witchers are powerful warriors like you'd find in other games, but that's not what makes them interesting/unique. Their specialties are knowledge of the many exotic monsters and their alchemy with potions (and traps and bombs in this case).
Reading/researching about creatures would be optional codex/lore in another game, but here it is part of the quests themselves. Potions, bombs, traps would be optional consumables in another game - and I personally rarely use them - but here they're critical.
Many people are struck by the difficulty of the game, and it's usually because they're trying to sword-fight their way through everything. If you really make use of the traps, bombs, potions, oils, etc. you should do just fine.
Lastly, understand that the character Geralt is not trying to be a heroic soldier. Unlike in comparable RPGs, you're neither a great hero nor villain, just something like a tough exterminator travelling from village to village cleaning up their monster infestations. Getting caught up in politics and wars is anathema to the cynical Witcher who just wants to be on his way to the next job.
They are actually quite different games although the second one naturally follows the storyline of it's predecessor. The first Witcher was more RPG heavy and didn't have any "press this button now or you die" sequences. Combat was also a bit more complicated with different stances available to the character. The witcher 2 is something between an RPG and an action game (but it is still very good) and easily beats Dragon Age 2 in terms of graphics.
There are references to the original story in the witcher 2 but you do not miss much if you do not know all the details.
