I certainly don't think its a good deal if you don't already have other tools using the battery and charger but it seems like a great deal if you already have everything else.
I have both Makitas 14.4 NiMH system and the 18 volt LXT system. I did notice Ryobi's Lithiums don't seem that much better but they do on the Makitas. My 18 volt, 3 amp hour Lithium is just a tad smaller than the 14.4 volt, 2.4 amp hour NiMH but it just over 1/2 the weight. Makita claims you should be able to get 4X as many charges as well.
When not in my drill or saws, my Makita batteries overdrive a ghetto 12 volt, 50 watt MR11 bike light. From what I've read, the 18 volts is 313% brighter than if it was on 12 volts. It does start to melt things if left on for a few minutes ... I'd love a clean HID light for the Makita