Great start for your first go at macro stuff, far better than my first attempts ;-)
Critique as follows
1. I think the composition could be a little better. Given the way the splash has hit the bottle top, I would aim for a more looking upward shot or more looking downward shot would have enhanced the rippled splash. I also think subject is not that interesting. You want to focus on the splash rather than the Pepsi logo. Try some using splashes onto fruit or perhaps cutlery or even glasses. I thought of a shot when I was washing up the other night when the water was hitting the side of a metal collinder, the bounce off the rim was really terrific. Have a look at my ones in a previous thread, each one took me about 100 shots to get what I wanted. I literally chose a nice fast shutter speed, used in-built flash and shot in RAW. The flash, although not the best was enough to light my subject and I literally, just took repeated shots as each splash hit the top of the spoon or knife. Shooting in RAW also meant, I could adjust the exposure and lighting. My method is by no means perfect but has been useful.
2. Great shot and composition. Only criticism is towards the subject, at first glance it looks like a pile of dog poop (the subject not your photo ;-) Again a different subject would make this a terrific shot.
3. Not sure if this is focussed properly. Again look out for composition, perhaps angle it so you can see the chain going through the hoop. Aim to get the chain nice and razor sharp and this will create a natural bokeh off the attached plastic thingie.
4/5. Again, composition. 4 is slightly out of focus, 5 is pretty good, although I would aim to look into the flower and see the water droplets coming off the side, you may also be able to get a refraction in the droplets.
Only last comment, is your borders are not consistent. Only a little thing, but it distracted me from your images.
This is by no means negative criticism - you will naturally get better, and I personally, have found critique on my photos to be really useful. In a few instances, I have actually taken the shot again and reposted to eventually get a much better image.
Keep the photos coming, I look forward to seeing some more of your stuff. Would be nice if a few others would post their images too.
EDIT: Try and submit a photo into the next Photo of the Month.
http://www.tekforums.co.uk/posts/list/11756.page