The 'L-series' is similar to the BlackBerry developer device that has already been released, with a 4.2", 768×1280 screen at 356ppi, while the 'N-series' provides an alternative for BlackBerry's traditional keyboard-loving market, with a 3" square, 720x720 display at 330ppi (which even at the lower resolution is still slightly better than the iPhone 4S' 326ppi). The L-series is slated for release in August, while keyboard lovers will apparently have to wait until early next year for the N-series.
Personally, I was hoping they'd release a phone with larger portrait screen and keyboard (either a portrait slider a la the BlackBerry Torch/Palm Pre or a candy bar like the Palm Pixi/Motorola Pro). But I guess 3" square at such a high resolution provides enough real estate to satisfy BlackBerry upgraders for the time being.
Potentially a bigger hiccup could be the issue of developer support for that aspect ratio, particularly when it comes to repackaged Android applications. Still, in combination with modified PlayBook applications I assume there will be enough stuff for early adopters to play around with.
Now that Palm is no more, RIM seems to be the only company left whose primary goal is to provide a true productivity/communication tool, with a focus on true multitasking, unobtrusive notifications and fast text input. For me and probably many others that's what I'm looking for in a phone, rather than how well it plays games or how many fart apps it has. Assuming all the other pieces of the puzzle are there (maps, smoothness of operation, etc.) I might be willing to help RIM stay afloat by giving them my money.