As many have commented already, this is a mellow album for the most part. If you are an original fan of the Goo Goo Dolls, you'll likely despise this effort. If you found the boys around the time of "A Boy Named Goo" and "Dizzy", you might like it, especially if your favorite songs are "Name" and "Black Balloon".
Personally, I'm fairly disappointed in the direction taken on this album. My favorite image of the Goo Goo Dolls is them rocking out to "Broadway" in the pouring rain on the DVD that came with the live album. I have always enjoyed the raw, energetic, Western New York attitude of these guys and how they bring it to the pop-rock world with great results.
With "Let Love In", the attitude has been mostly killed. There are several great tracks -- "Stay With You", "Let Love In", "Can't Let It Go", and "Give A Little Bit" (which most fans already have from the Live album). As much as I liked "Better Days" when it came out, it is just another ballad the way it is presented on this album. Worse, it feels lost in the middle of two melancholly ballads that offer very little to the album. "Beautiful", the last track, would be a standout song on any previous Goo album, but as with "Better Days" it gets drowned in mediocrity due to the numerous ballads/low energy songs on this album. Even Robbie has been tamed in this effort. Whether you like his singing or not, his songs are always fun and energetic. Not on this album -- "Listen" is merely passable, "Strangelove" is really bad. I don't care who sings these songs, they just aren't good songs to begin with.
IMHO, partnering with Glen Ballard was a big mistake. Time will tell if the Goo Goo Dolls are taking the path of so many pop-rock bands from the 80's in moving to ballad-heavy music later in their careers (e.g., Journey, REO Speedwagon, Night Ranger, Styx), or if they return to their roots and get back their Buffalo attitude and energy. I sincerely hope it's the latter, and that it doesn't take another 4 years to get the Goo Goo Dolls I enjoy so much back to form.
EDIT: After about 30 listenings, "We'll Be Here (When You're Gone)" has grown on me quite a bit. I've also noticed that if I just skip songs 3 and 5, the album is much better -- 4 stars without those tracks.