I actually don't care for using legendaries on my team. In the past, I would use them in order to defeat the elite four with ease. But, that got boring quickly, and I rarely used them in GSC and never used them from Hioenn onward. For me, they just spoil the game. So, that means I only value a legendary for its design especially since I don't use them.
Gen 1 had great designs. The storyline of the first two movies is superior to the crap that followed.
Gen 2 also great designs. Lugia and Ho Oh were a nice play on the legendary birds, and eveyone loves Celebi and legendary beasts.
Gen 3 Great with the exception of those legendary golems! Those are not pokemon! Also, this gen started adding too many legendaries, thus not making them as special. I sense they did this for more movie material.
Gen 4 Lots of super mega bulky pokemon that don't appeal to me, as well as lots of cutesy legendaries. The only ones I liked were shaymin, Cresselia, Arceus, and Darkrai. Manaphy, the lake trio, heatran, regigias, and the creation trio were dissappointing and unnecessary. WAY too many legendaries this time around.
Gen 5 This one is a mixed bag, I absolutely love the Swords of Justice, Reshiram and Zekrom, the animal formes of the Kami trio, and Victini. The rest, not so much. Vast improvement from gen 4.
Gen 6 Xerneas and Yvetal are by far my favorite legendaries thus far, and they are tempting me to use them!