Katsucon has been such a staple of my life that after my 19th Katsucon (and the 6th year at the Gaylord National) it's hard to write anything that's not already been said. If you haven't been to Katsucon, I can tell you it's a great convention from almost any angle -- except maybe price. There's a lot of food options in the area, and with some newer delis and grocery stores open now you'll have an alternative to pricier sit-down restaurants. Speaking of which, some of them aren't worth the price, so check reviews first. Hotels will be expensive, especially if you're at the Gaylord itself. Hotels in the vicinity are a short walk away and cost noticeably less, but depending on your attendance style (i.e. if you go to your room a lot to change or plan on making the walk late at night) may not be worth it. I always find the convenience of an on-site room worth it. Katsucon often gets very cold and windy, even moreso at night, and that short walk can feel pretty horrible without a full winter coat. Of course, the elevator battle is less intense outside the Gaylord, so that balances things out a little bit. For those who are new to conventions or still haven't figured this out after years of attending, packing your bags Sunday morning and taking them down at 7 am is worth it. If you're still up at that time, it's a good way to give your self some time to sleep in later on. Another tip, specifically for the Gaylord: the suites are very nice and come out to about the same price per person if you fill it up. I've had 10 in a suite before with plenty of room to spare. Likewise, the breakfast buffet is pricey but worth it for one day of the convention. Fill up once and you'll be good to go for a while.
Katsucon is really big on cosplay basically because of the gigantic atrium and upper-level "Gazebo" area. The lighting during the day really is spectacular. I tend to shoot without a flash while the light permits. The bright colors inside keep it all nice and crisp but you can avoid direct light and the shadows that come with them. Of course, everybody and their brother wants to shoot in the same area. You'll either have to be very patient, wait in line (if you want pictures in the Gazebo), or keep your pictures cropped to close-ups. I actually like this, but a lot of people will intentionally avoid the area due to crowding. Other parts of the convention area are conducive to photos, so groups with photoshoots may be better served by avoiding the Gazebo area. Sadly, at night the lighting becomes a lot more difficult. I actually switch to a smaller camera after the light goes away (which in February is around 6 pm). Katsucon also has a stricter policy with regards to any kind of "fixed" lighting, so anything with a tripod requires prior permission. This avoids some of the hassle of trying to maneuver around huge setups, but I see a number of people with pseudo-studios set up around the area, so it's possible.
As a mid-sized convention Katsucon has a pretty sizable dealer's room. Over the last decade merchants have shifted from the "staple" offerings like manga and VHS (and later DVD and bluray) to more "crafts" items like apparel and trinkets. This makes it look more like the artist's alley (which is also fairly big) but offers quite a bit of variety. Different vendors seem to have found their niches and specialties. For a while about anything you saw in the dealer's room you could get online. But as more and more merchandise has followed anime and gaming becoming more mainstream, you'll find stuff in person that you'll have difficulty finding online at a reasonable price. It's really become (once again) a haven of instant gratification.
What Katsucon isn't known for are huge guests or legendary panels, but that's not to say there aren't strong offerings. There's a lot of focus on fan interaction. Many of the guests are fan favorites who are happy to interact with attendees instead of rushing around from appearance to appearance as big-name guests are forced to do by their schedules. You'll be less likely to find directors and character designers there, but you will find dubbing talent, musical creators, and a lot of artists. All a lot more accessible to the fans. The lines for autographs and such aren't short but quite manageable. Unlike other places, they won't kill your entire day for a single autograph or sketch.
Two of the best offerings at Katsucon are the Anime Music Video contest and the Masquerade. Katsucon's AMVs have been pretty consistently worthwhile and with several showings you can easily catch it in different parts. You don't need the patience to sit through several hours and there's rarely one that isn't worth giving a shot. But the biggest event at any convention is the masquerade, and Katsucon certainly doesn't disappoint in this regard. Once again this year I was lucky to know many of the contestants. The show is well paced and the years of cumulative experience in running it (here's to you, Danny!) show. The event starts as on time as such a big event with so many people involved can, and at least from the audience's perspective tends to run smoothly. The entrants are also somewhat self-selecting and only a few entries tend to be groups without plan or practice. (Not that I'm judging, that's how I did most of my cosplay skits!) Only hitch this year were the furniture wranglers, who started breaking down the room in the middle of the awards. Luckily, that was put to a very quick stop. Congrats to Jez & co. for the Final Fantasy skit, amazing as always!
Perhaps the biggest draw for a larger number of attendees is the atmosphere conducive to partying and drinking. The hotel bar, despite closing fairly early at 11 pm or so, is a pretty good place to get drinks. People coming down from their rooms or back from dinner almost have to pass by and you'll catch anybody you're looking for if you stay there long enough. The suites, as mentioned, are very spacious and boast some rather great views of the Potomac river and Alexandria and Washington cities on the far side. The fountain area on the lowest level is also sometimes (but not always, oddly) a common area for revelers. And for those who wish to avoid the hotel, the weekends fill the National Harbor with a lot of nightlife. There's 20 or more establishments in the area happy to cater to the inclined clientele.
As always, the convention is what you make of it. Katsucon makes it easy to enjoy the weekend without a lot of pressure and yet plenty of opportunities to keep busy. It may not be the best for a day-trip visit, so consider staying at least one night. I'd recommend three, as the Friday morning traffic in the DC area can be epically terrible. There's something for everybody, so you should feel welcome at Katsucon.