I've been reading romance novels for a long time, but can't speak authoritatively on what women in the 20-30 age range like now. I can, however, list some romance novels I've liked that were popular, and thus I presume some of their audience is in your target range.
First, in defense of Janet Evanovich, the novel you tried to read is one of her early works, which has been out of print for years, perhaps deservedly. Because Evanovich is a Very Big Seller now, it was brought back into print along with several others of her early books. They are disappointing, and I agree with your evaluation. What has earned Evanovich her fame, fortune, and guaranteed spot in the NYT bestsellers list is the Stephanie Plum romantic mystery series, which are light, very funny, and fast-paced. These started with ONE FOR THE MONEY in 1994, followed by TWO FOR THE DOUGH (1996), and one every year since, with the most recent releases being TWELVE SHARP and PLUM LOVIN' (2006). I've read them all except PLUM LOVIN'.
I like the Stephanie Plum series for its humor and action; Stephanie is a lovable, sometimes loopy, heroine who is followed by disasters she barely manages to escape. She works for her cousin Vinnie as a bond enforcement agent, which creates a lot of the hilarity of the books by constantly putting her into weird situations. Evanovich has a talent for creating memorable comic characters, not just Stephanie but many of the secondary characters, such as Stephanie's sidekick Lula, a former ho' who nows works as a clerk in Vinnie's office; Stephanie's crazy grandmother, Grandma Mazur, who's a hoot; and many of the people Stephanie has to try to capture in her job. She also has two hunky men in her life, Morelli, a cop, and Ranger, another bond enforcement agent. Both are sexy but tough guys (no Fabios there!). I think you'd enjoy the Plum books a lot more than Evanovich's early romances. Also, the romance part of the novels is fairly minimal, because they are classed in the mystery genre rather than the romance genre. Try ONE FOR THE MONEY and see how you like it. Or, start later in the series--I recall being impressed that No. 9, TO THE NINES, was as funny as the first. (The scene with Lula and the pork chops slays me.)
I agree with Kate S on Jude Devereaux's A KNIGHT IN SHINING ARMOR--it was a favorite of mine for years. It's flawed as a novel in many ways, but has a central core fantasy that I think appeals to a lot of women. I must admit, however, that I haven't been able to finish any other Devereaux books I've started. (And, incidentally, despite Devereaux's having been one of the biggest-selling romance authors for years, she apparently doesn't have a website; I Googled her and got lots of references to her on other sites, but no site directly by/for her. Perhaps she's one of those cyber-phobic authors; I know a few who hate all things related to computers.)
Diana Gabaldon's OUTLANDER is one of my favorites. It's really more a historical novel/adventure story than a romance, although there is a strong romance at its core. I read the other books in the series, up through No. 4, but haven't tackled 5 & 6 yet (Gabaldon's books tend to be lo-o-o-ng). Although I liked the other books, OUTLANDER was the most satisfying to me. I consider Gabaldon a fine writer: excellent at character development, historical settings, and swashbuckling plots, as well as at describing realistic romantic relationships between men and women.
These are other historical romance writers whose work I love:
- Loretta Chase (LORD OF SCOUNDRELS is one of my all-time favorites);
- Laura Kinsale (FLOWERS FROM THE STORM is one of the finest historical romances ever written);
- Jo Beverley (the ones I like best are from her Malloren series--MY LADY NOTORIOUS, TEMPTING FORTUNE, SOMETHING WICKED, SECRETS OF THE NIGHT, DEVILISH);
- Mary Balogh (she had dozens of Regency romances published before she became a NYT bestseller with her Bedwyn series--the books whose titles start with SLIGHTLY...e.g., SLIGHTLY SCANDALOUS);
- Mary Jo Putney (THUNDER AND ROSES of her Company of Rogues series is probably my favorite; it was reprinted in 2003 and may still be available);
- Candice Proctor, who wrote wonderful atmospheric, character-driven historical romances (e.g., SEPTEMBER MOON) before switching to mysteries and a new pseudonym, C.S. Harris.
- Jennifer Crusie--light, rollicking, fast-paced (caution--like Evanovich, Crusie is so popular that her early work has been put back into print and, although well-written for their type, those books are not as satisfying or well-developed as her later, longer books, such as TELL ME LIES, CRAZY FOR YOU, WELCOME TO TEMPTATION, and subsequent work);
- Susan Elizabeth Phillips--she's good at character development, many of her novels feature pro athletes as heroes (e.g., IT HAD TO BE YOU and HEAVEN, TEXAS are probably my favorites), and her books also have strong notes of humor;
- Suzanne Brockmann--her Navy SEAL "Troubleshooters" series has put her on the bestseller lists, with exciting plots, strong characters, and headlong pacing (that series begins with THE UNSUNG HERO; the most recent title is INTO THE STORM, 10th in the series);
- J.D. Robb, a pseudonym used by Nora Roberts for her IN DEATH series featuring police lieutenant Eve Dallas. Those novels are edgy, urban, futuristic, and fun. I also like a lot of Roberts' more traditional romance novels (e.g., MONTANA SKY, which has been made into a TV movie that will air on the Lifetime channel on Monday, February 5. It remains to be seen how well the book-to-film transition is, but the picture features John Corbett as the hero, and he's a hottie).
I've reveled in the work of the authors listed above, however, and enjoyed most if not all they've written.