Our 6 month old wakes up between 3 and 5 times every night. She takes 2 or 3 naps a day (I wouldn't suggest playing around with her nap time.. better to let her get the rest she needs during the day) and is pretty much out for the night by 7/7:30. Between her bedtime and when she wakes for the day at 6:30, it's a nightmare! At this point, my husband and I have decided to simply wait it out. We've decided against any hard core sleep training (that's not to say that there aren't times we let her cry or fuss, or we soothe her without putting her to the breast, etc), and we're just waiting it out. Like your little one, ours also can play for up to 30 minutes in her crib, babbling, looking at her toes, etc, but eventually it turns in to fussing and crying, then outright screaming. I always thought by 6 months our baby would sleep through the night. She's breastfed and on solids but she doesn't take a bottle or pacifier...still, I thought the solids would fill up her belly and help her sleep longer. Now I know that it's a myth that solids help babies sleep longer (at least not our baby!).
You're fortunate that your first was such a great sleeper, so I can imagine it's difficult with your little girl. Hang in there and know you're not alone. I'm sorry I don't have any better answers---I think some babies just take longer than others.