Defending the planet is an angel's duty.
Also, shilling toys. Lots and lots of toys. Often times ugly toys that don't really connect to any of the themes and motifs in any particular way. Even during the ending credits of any given episode, which is normally safe from that sort of merchandising. Suffice to say, Tensou Sentai Goseiger is not one of the more popular sentais in the history of the franchise, and while there is good reason why, there are points where the series rises surprisingly high.
The first thing I want to talk about regarding the good and bad of this series is the characters. In the first place, they are "Gosei Angels" from the Gosei world, and they hail from one of three tribes, the Skick, the Landick, and the Seaick. The red and pink rangers, Alata and Eri, are from the Skick tribe, the black and yellow, Agri and Moune, are from the Landick tribe, and the blue ranger Hyde is the sole representative of the Seaick tribe. At first it seems as though mistrust, stereotypes, and prejudices between the various tribes will be a recurring, but this is quietly and unceremoniously dropped due mostly to Toei's mandate that the heroes not fight amongst themselves, which eliminates opportunities for character growth and development. There is some growth for Alata, Eri, and Moune, but nothing that really stands out in the franchise. Hyde had potential relating to how his partner, Magis, was killed before the start of the series, but that never gets fulfilled, and Agri never gets a set personality beyond "big strong guy". However, to backtrack a bit, I would like to talk about Alata; most red rangers in Super Sentai fall under one of two categories; the stoic mr. perfect, or the screaming idiot. Alata is neither; he is calm, cool, chillax sort of guy who goes with the flow and generally comes across like a little puppy dog...until the fighting begins, at which point he becomes an efficient and deadly killing machine. Its a very interesting combination of traits that actually manages to work.
Now, onto the villains. There are four groups of villains in Goseiger who appear in sequential order; The Warstar Aliens who look like giant bugs, The Yuumaju Monsters who dip into crypto-zoology for their designs and feed on pollution, The Matrintis who are robots, and Brajira the Messiah who is a fallen Gosei Angel. The progression from one group to the next is a thematic one, where the succeeding group has a stronger connection to our heroes and presents greater ethical conflicts and questions. On paper at any rate. In execution, the Warstar and the Yuumaju are dull and uninteresting with little in the way of anything to go for them, so for 32 episodes of the series, it's pretty tedious going with only the occasional bright spot going for it. However, once the Matrintis show up, things start tightening up, and by episode 39, things are consistently solid and progressing strongly with decent pacing, allowing the thematic strengths of the series to emerge, even if a bit late. Oh, and all the villains from the mooks on up are named after movies.
Finally, the merchandising. Sure, Super Sentai as a franchise is merchandise driven, but Goseiger takes it to really unfortunate extremes. For example, the Goseigers use cards from the Dice-O card game in Japan, and they have a robot buddy assistant...who just so happens to look exactly like a Dice-O arcade machine. It makes me think of the "Mattel and Mars Bar Chocobot Hour" from The Simpsons, and that was supposed to be a parody. Also, one of the mechs is an ostrich kicking around an egg like a soccer ball. Who thought that was a good idea?
So no, Goseiger is not one of the better sentais out there, and I would not recommend it as your first sentai. But, if you have a few under your belt, you may be equipped to endure its flaws to appreciate its merits.