Characters seem pretty easy to get in my opinion. Just for doing a run of the full story you get 200 splinters and 250G (store cash).
200 splinters may not seem like a lot but by the time you get it you will have another 100 splinters off just drops and thats halfway to the most expensive heroes (200/400/600 splinter cost). Right now just for logging in every day you get 3 odin marks (300 of these for a legendary item), 10 splinters and 5 cube shards (used to buy various items). There are also a few codes that work, HOLIDAYBOOSTS (Free 12 hour Rarity item finder - AKA BETTER ITEMS), IM3HRTBREAKER (Free iron man costume) and HULKLOVESHOLIDAYS (Free santa hulk costume).
Anyone that wants to start up should, its the perfect time to. With all the christmas freebies and the splinters / store cash you get, its pretty easy to get whatever hero you want.