[color=red][edit by mod: SPOILERS AHEAD][/color]
Because of its realistic and detailed art paired with a suspenseful and intriguing plot, this manga series is definitely one of the best. Even though some people found it lacking after a few of the manga, I think that it was necessary- what fun would it be if it ended quickly? Considering the intellects of both Light and L, it would be impossible to keep L unaware of Light's status as Kira. You can tell where his death was prolonged in the fifth volume, since Light and Misa both lost their memories at that point, helping L figure out who the new Kira was. Even though some fans also might've found the economic/business focus at this point annoying or boring, it was very important to set higher stakes for everyone, since neither Light nor L had the ability to manipulate anything in that time. It also set the scene for what everyone seems to have hated- the death of L. Personally, I thought that would be the end of the series; however, Ohba seemed to have had other plans. The orphanage twist was definitely a surprise, and, even though I found it in bad taste to introduce a character so similar to L (Near). However, I don't think he was a bad character in particular; I think that people saw him as such because of his similarities to L. Mello also set an interesting twist- someone who was supposed to be on the "good" side, trying to stop Kira, who also wanted to get rid of Near. Despite the whole "rivals" concept is a bit overdone at times in manga, it was very interesting to compare the two geniuses, since normal rivalries involve two people who are in no way alike. One example would be pitting a genius and someone who had to work for everything. However, these two were both geniuses going after a similar goal in their own ways because of the differences in moralities. And the introduction of yet another Kira increased the stakes for both sides. As it had in the beginning of the series, events eventually caused Light and Near to face each other... At what I would call the most suspenseful part of the manga, for obvious reasons. However, the actual "end" of the series did cause me slight disappointment, since it all ended so abruptly. Even so, it was a bit obvious since the beginning that it would end in such a way, or at least that it would end similarly, because, if it didn't, it would be difficult for the series to ever end. But, I did like the way the last chapter ended, since it helped to seem it all less abrupt, in a way.
Sorry for any spoilers, and for the length of the comment... I oftentimes have issues controlling my rants.