Plastic Chef Neelix
This page is dedicated to the general cooking fail that is Neelix.
Neelix does not respect the tastes of others
It is something that that many good chefs are known for is to tinker with recipes in order to improve upon them or to overcome a missing ingredient that isn't available. Neelix does not do this well and in fact he finds ways to force his own versions of dishes on those he is serving even when every part of the original recipe is available.  He seems to thank that no matter wht he is told that his special additions are always an improvement and is flummoxed at the very idea that someone could dislike his new version of the dish. This includes the additions of spices that he is constantly told that the patrons can't stand. This goes so far as to insist that when food is smuggled out of his kitchen because someone wanted to make a dish their way rather then his required some type of punishment.  It's understandable on a minor level that he would try to convince them that using locally available supplies are a worthwhile effort but if something does not please the pallet of a patron you shouldn't force it onto them. No this is not the same as convincing children to eat their vegetables, as the items he insists on adding are only flavor enhancers not items of any real nutritional value.
Neelix always cooks his food on high
It's someone understandable in the context of filming something cooking on screen to use an obviously visible flame but what we see Neelix doing goes well beyond that. In every cooking operation we see Neelix doing he is always doing so with the flames so high that fire licks up to sometimes half the height of the sides of the stop pot he is preparing sauce in. Something that any good cook will tell you is those kinds of heat levels are only useful in a vary narrow number of application, wok based cooking a good example. This goes to explain why we see Neelix overcooking or even outright burning food on multiple occasions. 
Neelix lacks even basic sauce making skills.
Neelix is seen in the episode, Learning Curve, to be making macaroni and cheese where his solution for making a cheese based sauce was to take a chunk of solid cheese and just toss it into a pot filled with macaroni and leave it at that. While with some soft young cheeses this is possible, even with those cheese and experience cook will melt the cheese into a separate saucepan and integrate it into a sauce then add that to the pasta. Also this is another place where his inability to ever turn down his burners will generally spell disaster as the pasta should be very over cooked before the cheese will become anything close to a stable sauce.
His high burners also means that when he is making a large amount of a spaghetti-type sauce he is required to make use of constant tending of the stew-pot that the sauce is cooking in in order to prevent it from burning. This is something that does not tend to produce a tomato sauce that will have much of anything that could be called good flavor or texture. This may be the reasons Tom Paris expressed annoyance at the quality of his Spaghetti.