The Limburgish language has several characteristics which differentiate it from other major West Germanic languages, in particular Dutch and German. This differentiation is related to a number of linguistic features, such as vocabulary and grammar, but also tonality and phonology.

Although the vocabulary of Limburgish has similarities with the vocabulary of Dutch and German, there are also significant differences. The vocabulary is closer to that of Rhenish, Limburgish’s linguistic neighbour, than that of Dutch. In addition, few of the words commonly used in Limburg can be found in the Woordenboek der Nederlandsche Taal (‘Dictionary of the Dutch Language’). Limburgish words were not included during the codification of the Dutch language, probably because these were seen as un-Dutch. Limburgish also preserves many West Germanic words that are no longer in use in Dutch or are seen as old-fashioned. In addition, the vocabulary of Limburgish also contains many words of Walloon origin.

The grammatical structures of Limburgish are also different to those of Dutch and are more similar to their German counterparts, but particularly resemble those of the adjacent Rhenish dialects.
The plurals and diminutives of nouns are often written with a dieresis, e.g. kop – köp – köpke (‘head – heads – small head’). This can also be seen in the conjugation of irregular verbs, in particular in the second or third person singular, e.g. iech kroep – diech krups – ’t krup (‘I crawl – you crawl – it crawls’).
For the past tense of regular verbs, Limburgish uses the ending –de, whereas Dutch uses the endings –de and –te, and German uses –te.
In addition, Limburgish also uses an optative (irrealis subjunctive) for the verb höbbe (‘to have’), which also exists in German but not in Dutch, e.g. Hej iech mer cent, daan kós ’ch m’ch e book koupe (‘If only I had money, then I would be able to buy myself a book’).
The gerund exists only in Limburgish. This is a verb form ending in –tere, which expresses the simultaneity of two actions, e.g. Zingentere lepe veer door de straote (‘While singing we walked through the streets’).
Indirect objects are also more frequently used in Limburgish than in other languages, e.g. iech koup miech e book (‘I buy myself a book).
This short summary outlines various grammatical features that are typical of all Limburgish expressions and which fundamentally distinguish the language from its linguistic neighbours, in particular Dutch.

One special characteristic of Limburgish is the language’s contrastive tonality, i.e. the use of two contrastive tones, a draw tone and a push tone, to create a difference in meaning. The meaning of words varies according to the tone with which such words are pronounced. Limburgish shares this tonality with several adjacent Rhenish dialects, but it is absent from Dutch and German. Although such tonality is a frequent occurrence within Asian languages, it is a rare feature in European languages.
The region where this contrastive tonality is used comprises almost the whole of Limburg. Notwithstanding the fact that each dialect of Limburgish has its own particular ‘tonal grammar’, the great majority of words use the same draw or push tone.
The semantic difference expressed by the use of tones may refer to a difference in the singular or the plural of the same word, e.g. ei bein (‘one leg’, with draw tone) – twie bein (‘two legs’, with push tone). The tonal difference may also indicate a completely different word. For example, veule with a draw tone is a verb and means ‘to feel’, but is a noun meaning ‘foal’ when pronounced with a push tone.

The phonology of Limburgish is also fundamentally different from that of Dutch and German. Vowels preserved from West Germanic have developed differently. In addition, Limburgish vocal structures have not been subject to some of the sound shifts that occurred in Dutch. Limburgish also contains vowels and diphthongs that do not exist in Dutch and German. However, several consonants of Limburgish have been subject to a High German consonant shift, such as from plosive (k) to fricative (ch), e.g. for the pronoun ‘I’: ik –> i(e)ch, and the adverb ‘also’: ook –> ouch.

References
Gussenhoven, C., De Limburgse tonen, in: Heijenrath, L., Kroon, S. (ed.), Vereniging Veldeke Limburg Jaarboek 2006, Veldeke Limburg, 2007, 21-32.
Hermans, B., The Composite Nature of Accent: With Case Studies of the Limburgian and Serbo-Croatian Pitch Accent, Amsterdam, 1994.
Keulen, R., Wijngaard, van de, T., Crompvoets, H., Walraven, F. (ed.), Riek van Klank; Inleiding in de Limburgse dialecten, Veldeke Limburg, 2007.
Werkgroep Erkenning Limburgs als Streektaal: Advies inzake de erkenning van het Limburgs als streektaal, 1996.