The truth is, unless you've been playing the game consistently, and for a good while, you're probably not going to get much out of Chains of Promathia. At the very least, in order to initiate the chain of events that will propel you through the best that Promathia to offer, you will have to have a job leveled to at least 30. On top of that, you'll have to be in a tight, efficient group in order to tackle the challenges that even the earliest Promathia missions will present. Indeed, many of the players I partied with during these scenarios had their main jobs leveled well into 50s and 60s, and even then, the missions proved plenty challenging. Not to say that players' levels are a direct indicator of their skill, but it's a decent enough measuring stick.
The creatures in the "Emptiness" zones are horrific indeed. Expect some loss of life (and levels).
In any case, Promathia's biggest draw is the number of new areas it introduces to the game. There is really a nice level of variety here, and those who enjoy exploring for its own sake will be thrilled, as many of these zones are richly detailed, and often densely populated. There isn't much in the way of new activities in these areas, barring a couple of fairly negligible cases, however -- "clamming" in Bibiki Bay, or riding the cool-looking, but awfully slow raft in Carpenters' Landing, for instance.
Sadly, none of these areas have thus far established themselves as "leveling spots," so apart form players en route to Promathia-specific events, or those simply out there on a lark, don't expect a whole lot of company. Many of these areas seem skewed towards high-level players, too, so unless you're able to take on fairly strong enemies solo (or just brave or foolhardy), leisurely treks aren't advised. That said, there's nothing stopping intrepid players from forming groups, and engaging in leveling sessions in these new areas. It's even possible to do so at relatively low levels -- for example, the outer edges of Carpenters' Landing can sustain parties in their low to mid 20s -- but as anyone who's played FFXI knows, forming a balanced party is challenging enough. Getting it to venture outside of the established leveling spots, meanwhile, is often comparable to pulling teeth.